add changelog entry

Author: schloerke

CHANGELOG.md

@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * Both `ui.Chat()` and `ui.MarkdownStream()` now support arbirary Shiny UI elements inside of messages. This allows for gathering input from the user (e.g., `ui.input_select()`), displaying of rich output (e.g., `render.DataGrid()`), and more. (#1868)
 
+* Added support for `session.on_end(fn)` which registers callbacks that will execute just before attempting to close the websocket. (#1930)
+
 ### Changes
 
 * Express mode's `app_opts()` requires all arguments to be keyword-only. If you are using positional arguments, you will need to update your code. (#1895)