Added Gitter badge

Author: gitter-badger

README.md

@@ -1,5 +1,7 @@
 # react-bootstrap
 
+[![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/react-bootstrap/react-bootstrap?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+
 [Bootstrap 3](http://getbootstrap.com) components built with [React](http://facebook.github.io/react/)
 
 [![Build Status](https://travis-ci.org/react-bootstrap/react-bootstrap.svg)](https://travis-ci.org/react-bootstrap/react-bootstrap) [![NPM version](https://badge.fury.io/js/react-bootstrap.svg)](http://badge.fury.io/js/react-bootstrap) [![Bower version](https://badge.fury.io/bo/react-bootstrap.svg)](http://badge.fury.io/bo/react-bootstrap)