added docker file permission instructions.

README.md

@@ -154,6 +154,11 @@ ipfs files that will persist when you restart the container.
 
     export ipfs_staging=</absolute/path/to/somewhere/>
     export ipfs_data=</absolute/path/to/somewhere_else/>
+    
+Make these folders accesible from docker:
+
+    sudo chmod -R 777 /absolute/path/to/somewhere/
+    sudo chmod -R 777 /absolute/path/to/somewhere_else/
 
 Start a container running ipfs and expose ports 4001, 5001 and 8080: