Added changelog entry.

Author: nickmelnikov82

Diff for: CHANGELOG.md

@@ -2,6 +2,9 @@
 All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](https://semver.org/).
 
+### Fixed
+- [#1976](https://github.com/plotly/dash/pull/1976) Fix bug [#1962](https://github.com/plotly/dash/issues/1962) in which DatePickerSingle and DatePickerRange are extremely slow when provided a long list of disabled_days.
+
 ## [2.3.1] - 2022-03-29
 
 ### Fixed