Update CHANGELOG.md

ScriptableRenderPipeline/HDRenderPipeline/CHANGELOG.md

 
 ## [2018.2 undecided]
 
+### Improvements
+- Add stripper of shader variant when building a player. Save shader compile time.
+- Disable per-object culling that was executed in C++ in HD whereas it was not used (Optimization)
+- Enable texture streaming debugging (was not working before 2018.2)
+
 ## [2018.1 undecided]
 
 ### Improvements