Update CHANGELOG.md

Author: JenniferDUnity

com.unity.postprocessing/CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this package will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## [3.5.3] - 2026-03-12
+
+### Fixed
+- Documentation updates
+
 ## [3.5.2] - 2025-12-17
 
 ### Fixed