Updating changelog for 0.4.0 release (#76)

Author: JonathanHUnity

com.unity.perception/CHANGELOG.md

@@ -7,6 +7,18 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+
+### Changed
+
+### Deprecated
+
+### Removed
+
+### Fixed
+
+## [0.4.0-preview.1] - 2020-08-07
+
 ### Added
 Added new randomization tools