Add PYTHONHASHSEED into changelog

Author: msimacek

CHANGELOG.md

@@ -5,6 +5,7 @@ language runtime. The main focus is on user-observable behavior of the engine.
 
 ## Version 22.0.0
 * Added support for `pyexpat` module.
+* Added partial support for `PYTHONHASHSEED` environment variable (also available via `HashSeed` context option), currently only affecting hashing in `pyexpat` module.
 
 ## Version 21.3.0