add changelog

Author: KoolADE85

CHANGELOG.md

@@ -10,6 +10,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## Fixed
 - [#3629](https://github.com/plotly/dash/pull/3629) Fix date pickers not showing date when initially rendered in a hidden container.
 - [#3627][(](https://github.com/plotly/dash/pull/3627)) Make dropdowns searchable wheen focused, without requiring to open them first
+- [#3656][(](https://github.com/plotly/dash/pull/3656)) Improved dropdown performance for large collections of options