Add changelog note for rollout

Author: henrymercer

CHANGELOG.md

@@ -7,6 +7,7 @@ See the [releases page](https://github.com/github/codeql-action/releases) for th
 - Log a warning if the amount of available disk space runs low during a code scanning run. [#1825](https://github.com/github/codeql-action/pull/1825)
 - When downloading CodeQL bundle version 2.13.4 and later, cache these bundles in the Actions tool cache using a simpler version number. [#1832](https://github.com/github/codeql-action/pull/1832)
 - Fix an issue that first appeared in CodeQL Action v2.21.2 that prevented CodeQL invocations from being logged. [#1833](https://github.com/github/codeql-action/pull/1833)
+- We are rolling out a feature in August 2023 that will improve the quality of file coverage information. [#1835](https://github.com/github/codeql-action/pull/1835)
 
 ## 2.21.3 - 08 Aug 2023