Update CHANGELOG

Author: BenGraterUnity

com.unity.postprocessing/CHANGELOG.md

@@ -4,11 +4,12 @@ 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).
 
-## [Unreleased]
+## [3.5.2] - 2025-12-17
 
 ### Fixed
 - Fixed obsolete ProjectWindow usage in Unity 6.4 or newer
 - Replaced deprecated Mono API with CoreCLR-compatible API
+- Documentation updates
 
 ## [3.5.1] - 2025-09-19