docs(): adding links to support channels

Author: jamesdaniels

README.md

@@ -22,6 +22,8 @@ Status: Release candidate
 
 [Upgrading to v5.0? Check out our guide.](docs/version-5-upgrade.md)
 
+**Having troubles?** Get help on the [Firebase Mailing List](https://groups.google.com/forum/#!forum/firebase-talk) (offically supported), the [Firebase Community Slack](https://firebase.community/) (look for the `#angularfire2` room), [Gitter](https://gitter.im/angular/angularfire2), or [Stack Overflow](https://stackoverflow.com/questions/tagged/angularfire2).
+
 ## Install
 
 ```bash