UPGRADING.md in slack-ruby-bot-server-0.8.3 vs UPGRADING.md in slack-ruby-bot-server-0.9.0

@@ -1,7 +1,15 @@
 Upgrading Slack-Ruby-Bot-Server
 ===============================
 
+### Upgrading to >= 0.9.0
+
+### Removed Ping Worker
+
+The ping worker that was added in 0.7.0 has been removed in favor of a lower level implementation in slack-ruby-client. Remove any references to `ping` options.
+
+See [slack-ruby-client#226](https://github.com/slack-ruby/slack-ruby-client/pull/226) and [#93](https://github.com/slack-ruby/slack-ruby-bot-server/pull/93) for more information.
+
 ### Upgrading to >= 0.8.0
 
 ### Different Asynchronous I/O Library
 
 The library now uses [async-websocket](https://github.com/socketry/async-websocket) instead of [celluloid-io](https://github.com/celluloid/celluloid-io). If your application is built on Celluloid you may need to make changes and use `Async::Reactor.run` and the likes.