Add Gitter badge

README.md

@@ -3,6 +3,8 @@
 crowi-plus
 ===========
 
+[![Join the chat at https://gitter.im/weseek/crowi-plus](https://badges.gitter.im/weseek/crowi-plus.svg)](https://gitter.im/weseek/crowi-plus?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+
 [![Deploy](https://www.herokucdn.com/deploy/button.png)](https://heroku.com/deploy?template=https://github.com/weseek/crowi-plus/tree/v1.0.0-RC2)
 
 [![wercker status](https://app.wercker.com/status/39cdc49d067d65c39cb35d52ceae6dc1/s/master "wercker status")](https://app.wercker.com/project/byKey/39cdc49d067d65c39cb35d52ceae6dc1)