[README.md] added gitter badge

README.md

@@ -3,6 +3,8 @@
 
 [![Build Status](https://travis-ci.org/source-foundry/Hack.svg?branch=master)](https://travis-ci.org/source-foundry/Hack) [![Contributors](https://img.shields.io/badge/contributors-125-orange.svg?style=flat)](https://github.com/source-foundry/Hack/blob/master/docs/CONTRIBUTORS.md)
 
+[![Join the chat at https://gitter.im/source-foundry/Hack](https://badges.gitter.im/source-foundry/Hack.svg)](https://gitter.im/source-foundry/Hack)
+
 Hack v3 is here!  [Click here to learn what's new](https://medium.com/source-words/hack-typeface-v3-6943991c1a80).
 
 ### A typeface designed for source code