add coveralls status to readme

README.md

@@ -1,4 +1,8 @@
-# melody [![Build Status](https://travis-ci.org/olahol/melody.svg)](https://travis-ci.org/olahol/melody) [![GoDoc](https://godoc.org/github.com/olahol/melody?status.svg)](https://godoc.org/github.com/olahol/melody)
+# melody
+
+[![Build Status](https://travis-ci.org/olahol/melody.svg)](https://travis-ci.org/olahol/melody)
+[![Coverage Status](https://img.shields.io/coveralls/olahol/melody?style=flat)](https://coveralls.io/r/olahol/melody)
+[![GoDoc](https://godoc.org/github.com/olahol/melody?status.svg)](https://godoc.org/github.com/olahol/melody)
 
 > :notes: Minimalist websocket framework for Go.