Add link to ASF HipChat NiFi room in README.
This closes:
@@ -123,8 +123,8 @@ To run NiFi:
## Getting Help
If you have questions, you can reach out to our mailing list: dev@nifi.apache.org
([archive](http://mail-archives.apache.org/mod_mbox/nifi-dev)).
-We're also often available in IRC: #nifi on
-[irc.freenode.net](http://webchat.freenode.net/?channels=#nifi).
+For more interactive conversations and chat, we're also often available in IRC: #nifi on
+[irc.freenode.net](http://webchat.freenode.net/?channels=#nifi) and in #NiFi on [ASF HipChat](https://www.hipchat.com/gzh2m5YML).
## Documentation
