add link to mailing list

README.md

@@ -3,6 +3,7 @@
 go-github is Go client library for accessing the [GitHub API][].
 
 **Documentation:** <http://godoc.org/github.com/google/go-github/github>  
+**Mailing List:** [go-github@googlegroups.com](https://groups.google.com/group/go-github)
 **Build Status:** [![Build Status](https://travis-ci.org/google/go-github.png?branch=master)](https://travis-ci.org/google/go-github)  
 **Test Coverage:** [![Test Coverage](https://coveralls.io/repos/google/go-github/badge.png?branch=master)](https://coveralls.io/r/google/go-github?branch=master) ([gocov report](https://drone.io/github.com/google/go-github/files/coverage.html))