docs: Add changelog item

Author: gadenbuie

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [UNRELEASED]
 
+### New features
+
+* 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)
+
 ### Bug fixes
 
 * `ui.Chat()` now correctly handles new `ollama.chat()` return value introduced in `ollama` v0.4. (#1787)