Updated CHANGELOG.md

com.unity.render-pipelines.lightweight/CHANGELOG.md

 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [3.0.1-preview]
+### Changed
+- Terrain shader optimizations.
 
 ## [3.0.0-preview]
 ### Added