readme: add godoc badge

Author: vmihailenco

README.md

@@ -1,4 +1,7 @@
-# Redis client for Golang [![Build Status](https://travis-ci.org/go-redis/redis.png?branch=master)](https://travis-ci.org/go-redis/redis)
+# Redis client for Golang
+
+[![Build Status](https://travis-ci.org/go-redis/redis.png?branch=master)](https://travis-ci.org/go-redis/redis)
+[![GoDoc](https://godoc.org/github.com/go-redis/redis?status.svg)](https://godoc.org/github.com/go-redis/redis)
 
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