Added Gitter badge

README.md

@@ -7,6 +7,8 @@ Follow the link for more information: [http://c3js.org](http://c3js.org/)
 
 ## Tutorial and Examples
 
+[![Join the chat at https://gitter.im/masayuki0812/c3](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/masayuki0812/c3?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+
 + [Getting Started](http://c3js.org/gettingstarted.html)
 + [Examples](http://c3js.org/examples.html)