Update changelog

Author: cpsievert

CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### New features
 
+* Added a new `ui.MarkdownStream()` component for performantly streaming in chunks of markdown/html strings into the UI. This component is primarily useful for text-based generative AI where responses are received incrementally. (#1782)
+
 * Added a new `.add_sass_layer_file()` method to `ui.Theme` that supports reading a Sass file with layer boundary comments, e.g. `/*-- scss:defaults --*/`. This format [is supported by Quarto](https://quarto.org/docs/output-formats/html-themes-more.html#bootstrap-bootswatch-layering) and makes it easier to store Sass rules and declarations that need to be woven into Shiny's Sass Bootstrap files. (#1790)
 
 * The `ui.Chat()` component's `.on_user_submit()` decorator method now passes the user input to the decorated function. This makes it a bit more obvious how to access the user input inside the decorated function. See the new templates (mentioned below) for examples. (#1801)