Update CHANGELOG.md

com.unity.perception/CHANGELOG.md

 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
+
+### Added
+
+### Changed
+
+### Deprecated
+
+### Removed
+
+### Fixed
+
 ## [0.6.0-preview.1] - 2020-12-03
 
 ### Added