docs: update contact info (envoyproxy#42)

README.md

@@ -354,5 +354,13 @@ You can specify the debug port with the `DEBUG_PORT` environment variable. It de
 
 # Contact
 
-* [#lyft-envoy](http://webchat.freenode.net/?channels=lyft-envoy): IRC
-* [lyft/envoy](https://gitter.im/lyft/envoy): Gitter
+* [envoy-announce](https://groups.google.com/forum/#!forum/envoy-announce): Low frequency mailing
+  list where we will email announcements only.
+* [envoy-users](https://groups.google.com/forum/#!forum/envoy-users): General user discussion.
+  Please add `[ratelimit]` to the email subject.
+* [envoy-dev](https://groups.google.com/forum/#!forum/envoy-dev): Envoy developer discussion (APIs,
+  feature design, etc.). Please add `[ratelimit]` to the email subject.
+* [Slack](https://envoyproxy.slack.com/): Slack, to get invited go [here](http://envoyslack.cncf.io).
+  We have the IRC/XMPP gateways enabled if you prefer either of those. Once an account is created,
+  connection instructions for IRC/XMPP can be found [here](https://envoyproxy.slack.com/account/gateways).
+  The `#ratelimit-users` channel is used for discussions about the ratelimit service.