Add changelog entry

Author: redsun82

CHANGELOG.md

@@ -4,7 +4,7 @@ See the [releases page](https://github.com/github/codeql-action/releases) for th
 
 ## [UNRELEASED]
 
-No user facing changes.
+- We are rolling out a feature in October 2023 that will improve the success rate of C/C++ autobuild. [#1889](https://github.com/github/codeql-action/pull/1889)
 
 ## 2.21.8 - 19 Sep 2023