update changelog for optimistic chat posting

I can't no longer push straight to develop so updating changelog is a bit of a pain

CHANGELOG.md

@@ -21,6 +21,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Added
 - Import/export a muted users
 - Proper handling of deletes when using websocket streaming
+- Added optimistic chat message sending, so you can start writing next message before the previous one has been sent
 
 ## [2.1.1] - 2020-09-08
 ### Changed