docs: add notes on snap build and publish

License: MIT
Signed-off-by: Oli Evans <oli@tableflip.io>

docs/snap.md

+# Publishing go-ipfs as a snap
+
+> Snap is the default package manager for ubuntu since the release of 20.04. This doc captures what we know about building go-ipfs as a snap packge and publishing it to the snapstore.
+
+The go-ipfs snap is defined in [snap/snapcraft.yaml](https://github.com/ipfs/go-ipfs/blob/master/snap/snapcraft.yaml). For more detail on our snapcraft.yaml see: https://github.com/ipfs-shipyard/ipfs-snap
+
+- go-ipfs is published as `ipfs` to the snapcraft store, see: https://snapcraft.io/ipfs
+- ipfs-desktop is published as `ipfs-desktop`, from CI, here: https://github.com/ipfs-shipyard/ipfs-desktop/blob/master/.github/workflows/snapcraft.yml
+
+For go-ipfs we deliberately lean on the Canonical lauchpad.net build environment so as it simplifies creating builds for more architectures, which has been requested by user numerous times.
+
+Linux user can install go-ipfs with:
+
+```
+$ snap install ipfs
+```
+
+Apps installed via Snapcraft are auto-updating by default. Snapcraft uses 'Release Channels' to let the user pick their stability level, with channels for `stable`, `candidate`, `beta` and `edge`. Snap will install the lasest release from the `stable` channel by default. A user that wants to test out the bleeding edge can opt in by passing the `--edge` flag
+
+```
+$ snap install --edge ipfs
+```
+
+<img width="1072" alt="Dashboard for managaing go-ipfs snap release channels for go-ipfs" src="https://user-images.githubusercontent.com/58871/95761096-bcb34580-0ca3-11eb-8ce7-2496b2456335.png">
+
+## Known issues
+
+- `ipfs mount` fails as fusermount is not included in the snap, and cannot work from a snap as it is not able to create non-root mounts, see: https://github.com/elopio/ipfs-snap/issues/6
+
+```console
+ubuntu@primary:~$ ipfs mount
+2020-07-10T09:54:17.458+0100	ERROR	node	node/mount_unix.go:91	error mounting: fusermount: exec: "fusermount": executable file not found in $PATH
+2020-07-10T09:54:17.463+0100	ERROR	node	node/mount_unix.go:95	error mounting: fusermount: exec: "fusermount": executable file not found in $PATH
+```
+
+## Developing
+
+We let launchpad.net build our snap for us, but if you need to edit the snapcraft.yml you can test it locally
+
+### Requirements
+
+ You need `snapcraft` installed locally
+
+```console
+# ubuntu or similar
+$ snap install snapcraft --classic
+
+# macos
+$ brew install snapcraft
+```
+
+### Build and test
+
+**Build** out a snap package for go-ipfs by running the following from this project
+
+```console
+$ snapcraft
+```
+
+**Test** the built snap package by installing it on a system that has `snapd`
+
+```
+$ snap install ipfs_<snap details here>.snap
+# then kick the tires
+$ ubuntu@primary:~$ ipfs daemon
+Initializing daemon...
+go-ipfs version: 0.7.0-dev
+```
+
+You can test it out on mac too. By installing and using `snapcraft`, it'll pull in `multipass` which is a quick way to run an ubuntu vm, and it has a notion of a primary container, which gets nice things like automounting your home dir in the vm, so you can:
+
+```console
+# install your .snap in a multipass vm
+$ multipass shell
+ubuntu@primary:~$ cd ~/Home/path/to/snap/on/host/filesystem
+ubuntu@primary:~$ snap install ipfs_<snap details>.snap --devmode --dangerous
+ubuntu@primary:~$ ipfs daemon
+Initializing daemon...
+go-ipfs version: 0.7.0-dev
+```
+
+### Building in Docker
+
+[ipfs-shipyard/ipfs-snap](https://github.com/ipfs-shipyard/ipfs-snap) includes a Dockerfile that creates an image that can build go-ipfs from source and package it as a snap. It starts with `snapcore/snapcraft:stable` and adds in `go` and just enough tools to allow snapcraft to build go-ipfs. It is published to dockerhub as `ipfs/ipfs-snap-builder`.
+
+```console
+$ docker run -v $(pwd):/my-snap ipfs/ipfs-snap-builder:latest sh -c "apt update && cd /my-snap && snapcraft --debug"
+```
+
+## Publishing the Snap
+
+The following snap release channels are published automatically:
+
+| Git branch | Snap channel |
+|------------|--------------|
+| `release`  | `stable`
+| `master`   | `edge`
+
+
+### Edge via snapcraft.io
+
+The snapcraft store watches the default branch of the go-ipfs repo, and updates the snap for the `edge` channel. This service is configured automatically by snapcraft. It's neat, but it doesn't allow us to watch any branch other than the default.
+
+<img width="1072" alt="Screenshot 2020-10-12 at 15 56 07" src="https://user-images.githubusercontent.com/58871/95761075-b755fb00-0ca3-11eb-99d4-95e5f42cb48a.png">
+
+
+### Stable via launchpad.net
+
+The `stable` channel is published automatically via launchpad.net. There is a mirror of the go-ipfs repo at https://launchpad.net/go-ipfs that is sync'd with the github repo every few hours (at canonical's leisure).
+
+A snap build configuration called `ipfs-stable` is set up to watch the `release` branch on go-ipfs and publish it to the `stable` snap channel.
+
+The key configuration points are:
+
+```yaml
+# What flavour VM to build on.
+Series: infer from snapcraft.yml
+
+Source:
+    Git:
+        # the launchpad mirror of go-ipfs
+        Git repository: ~ipfs/go-ipfs/+git/go-ipfs
+        Git branch: refs/heads/release
+
+Automatically build when branch changes: true
+    Source snap channels for automatic builds:
+        # tell snapcraft what version of snapcraft to use when building.
+        # NOTE: At time of writing we use the default `core18` platform for the 
+        # go-ipfs snap. If you specify others here, a build error occurs, which 
+        # I think is mainly due to a launchpad ux bug here.
+        core: ""
+        core18: stable
+        core20: ""
+        snapcraft: stable
+
+
+Automatically upload to store:
+    Registered store package name: ipfs
+    Store channels:
+        Risk: 
+            Stable: true
+
+# What architectures to build for. this selection is chosen to match the auto 
+# configured build provided by snapcraft for the edge channel, for neatness, so 
+# that all architectures that currently have builds in snap continue to get 
+# updates, even though some of them would be tough for use to test on.
+Processors:
+    amd64: true
+    # raspi 4
+    arm64: true
+    # older raspi
+    armhf: true
+    # sure ok i guess.
+    i386: true
+    # hmmm... PowerPC!?
+    ppc64el: true
+    # wat. IBM system Z mainframes!?
+    s390x: true
+```
+
+![Screenshot_2020-10-12 Edit ipfs-stable Snap packages “IPFS Maintainers” team](https://user-images.githubusercontent.com/58871/95762510-b4f4a080-0ca5-11eb-8148-d208f891d202.png)
+
+### Future work - Publish RCs to the `candidate` channel
+
+If we wish to publish release candidates to the snap store, we can do that by creating a new snap build config
+
+1. Find the `release-vX.X` branch in the lauchpad.net mirror of the go-ipfs repo.
+    - e.g. https://code.launchpad.net/~ipfs/go-ipfs/+git/go-ipfs/+ref/release-v0.7.0
+2. Click "Create snap package"
+3. Fill out the form using the same values as listed above for the stable channel, but:
+    - Set `Name` to `ipfs-candidate` _(this just needs to be a unique name to identify this config)_
+    - For `Risk` select only `Candidate` _(so the snap is published to the `Candidate` channel.)_
+
+You can trigger a build manually to kick things off. Subsequent changes to that branch will be published as a snap automatically when when the mirror next syncs with github (every 6-12hrs)
+
+
+## Who can edit this?
+
+The `ipfs` snapcraft.io listing can be edited by
+
+- @elopio _TBC, the original submitter, need to check about getting ownership transferred._
+- @lidel
+- @olizilla
+
+You need a Canonical developer account, then ask an existing owner to add you. Accsess is managed here https://dashboard.snapcraft.io/snaps/ipfs/collaboration/
+
+
+The launchpad.net config is managed by [**IPFS Maintainers**](https://launchpad.net/~ipfs) team, and you can request to join that team with your Canonical developer acccount. The list of maintainers is here: https://launchpad.net/~ipfs/+members
+
+At the time of writing the launchpad maintainers are:
+
+- @lidel
+- @olizilla
+
+
+## References
+
+- Walkthrough of publishing a snap package via snapcraft and launchpad: https://www.youtube.com/watch?v=X_U-pcvBFrU
+- For more details on the go-ipfs snapcraft.yaml see: https://github.com/ipfs-shipyard/ipfs-snap
+- publishing to multiple channels via build.snapcraft.io: https://forum.snapcraft.io/t/maintaining-and-publishing-multiple-to-multiple-channels-via-build-snapcraft-io/12455
+- How node.js manages snaps: https://github.com/ipfs/go-ipfs/issues/7679#issuecomment-695914986