Update CHANGELOG.md

Author: schloerke

CHANGELOG.md

@@ -9,6 +9,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## New features
 
+* Added support for bookmarking Shiny applications. Bookmarking allows users to save the current state of an application and return to it later. This feature is available in both Shiny Core and Shiny Express. (#1870, #1915, #1919, #1920, #1922, #1934, #1938, #1945, #1951)
+  * To enable bookmarking in Express mode, set `shiny.express.app_opts(bookmark_store=)` during the app's initial construction.
+  * To enable bookmarking in Core mode, set `shiny.App(bookmark_store=)` when constructing the `app` object.
+
 * 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 a new `.message_stream_context()` method to `ui.Chat()`. This context manager is a useful alternative to `.append_message_stream()` when you want to: (1) Nest a stream within another and/or