message: Add information about Slack
diff: @@ -34,10 +34,9 @@ to find out more about the origin story and design philosophy of Envoy.
  feature design, etc.).
  * [envoy-maintainers](https://groups.google.com/forum/#!forum/envoy-maintainers): Use this list
  to reach all core Envoy maintainers.
  -* [#lyft-envoy](http://webchat.freenode.net/?channels=lyft-envoy): IRC (synced to Gitter).
  * [Twitter](https://twitter.com/EnvoyProxy/): Follow along on Twitter!
  -* [lyft/envoy](https://gitter.im/lyft/envoy): Gitter (most people use Gitter. NOTE: Response to user
  - questions is best effort on Gitter. For a "guaranteed" response please email envoy-users@ per the
  +* [Slack](https://envoyproxy.slack.com/): Slack, to get invited go here: http://envoyslack.cncf.io (NOTE: Response to user
  + questions is best effort on Slack. For a "guaranteed" response please email envoy-users@ per the
  guidance in the following linked thread.).
  Please see [this](https://groups.google.com/forum/#!topic/envoy-announce/l9zjYsnS3TY) email thread
  