feat(README): add community contact points

Add the sig-apps mailing list, developer call details, and #helm slack
channel.

Based on https://github.com/kubernetes/kubernetes-template-project/blob/master/README.md

README.md

@@ -40,3 +40,11 @@ Download a [release tarball of helm for your platform](https://github.com/kubern
 	- [Chart Repository Guide](docs/chart_repository.md)
 	- [Syncing your Chart Repository](docs/chart_repository_sync_example.md)
 - [Developers](docs/developers.md)
+
+## Community, discussion, contribution, and support
+
+You can reach the Helm community and developers via the following channels:
+
+- [Kubernetes Slack](https://slack.k8s.io): #helm
+- Mailing List: https://groups.google.com/forum/#!forum/kubernetes-sig-apps
+- Developer Call: Thursdays at 9:30-10:00 Pacific. https://engineyard.zoom.us/j/366425549