Add link to gitter chat room

Author: garious

README.md

@@ -1,6 +1,8 @@
 The Flake Build System
 ======================
 
+[![Join the chat at https://gitter.im/garious/flake](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/garious/flake?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+
 [![Build Status](https://travis-ci.org/garious/flake.svg)](https://travis-ci.org/garious/flake)
 
 Introduction