Update the changelog

com.unity.render-pipelines.high-definition/CHANGELOG.md

 
 ## [3.4.0-preview]
 
+### Added
+ - Added controls for linear fade at the boundary of density volumes
+
 ### Fixed
 - Stencil test during decals normal buffer update is now properly applied
 - Fixed an issue where sometimes the deferred shadow texture would not be valid, causing wrong rendering.