Update README.md add test coverage badge

README.md

 # cidranger
-Fast IP to CIDR block(s) lookup using trie in Golang, inspired by [IPv4 route lookup linux](https://vincent.bernat.im/en/blog/2017-ipv4-route-lookup-linux).
+Fast IP to CIDR block(s) lookup using trie in Golang, inspired by [IPv4 route lookup linux](https://vincent.bernat.im/en/blog/2017-ipv4-route-lookup-linux).  Possible use cases include detecting if a IP address is from published cloud provider CIDR blocks (e.g. 52.95.110.1 is contained in published AWS Route53 CIDR 52.95.110.0/24), IP routing rules, etc.
 
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+[![Coverage Status](https://img.shields.io/coveralls/yl2chen/cidranger.svg?branch=master&style=flat-square)](https://coveralls.io/github/yl2chen/cidranger?branch=master)
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-Trie storing CIDR blocks `128.0.0.0/2` `192.0.0.0/2` `200.0.0.5` without path compression.
+This is visualization of a trie storing CIDR blocks `128.0.0.0/2` `192.0.0.0/2` `200.0.0.5` without path compression, the 0/1 number on the path indicates the bit value of the IP address at specified bit position, hence the path from root node to a child node represents a CIDR block that contains all IP ranges of its children, and children's children.
 <p align="left"><img src="http://i.imgur.com/vSKTEBb.png" width="600" /></p>
 
-Trie storing same CIDR blocks with path compression, improving both lookup speed and memory footprint.
+Visualization of trie storing same CIDR blocks with path compression, improving both lookup speed and memory footprint.
 <p align="left"><img src="http://i.imgur.com/JtaDlD4.png" width="600" /></p>
 
 ## Getting Started
@@ -49,13 +50,14 @@ containingNetworks, err = ranger.ContainingNetworks(net.ParseIP("128.168.1.0"))
 ```
 
 ## Benchmark
-Compare hit/miss case for IPv4/IPv6 using PC trie vs brute force implementation, Ranger is initialized with published AWS ip ranges.
+Compare hit/miss case for IPv4/IPv6 using PC trie vs brute force implementation, Ranger is initialized with published AWS ip ranges (889 IPv4 CIDR blocks and 360 IPv6)
 ```go
 // Ipv4 lookup hit scenario
 BenchmarkPCTrieHitIPv4UsingAWSRanges-4         	 5000000	       353   ns/op
 BenchmarkBruteRangerHitIPv4UsingAWSRanges-4    	  100000	     13719   ns/op
 
-// Ipv6 lookup hit scenario
+// Ipv6 lookup hit scenario, counter-intuitively faster then IPv4 due to less IPv6 CIDR
+// blocks in the AWS dataset, hence the constructed trie has less path splits and depth.
 BenchmarkPCTrieHitIPv6UsingAWSRanges-4         	10000000	       143   ns/op
 BenchmarkBruteRangerHitIPv6UsingAWSRanges-4    	  300000	      5178   ns/op