Update CHANGES.md

Author: tumbarumba

CHANGES.md

@@ -5,6 +5,8 @@
 ### Improvements
 
 * Javadoc improvements and cleanup ([PR #420](https://github.com/hamcrest/JavaHamcrest/pull/420))
+* Optional matchers ([PR #421](https://github.com/hamcrest/JavaHamcrest/pull/421))
+* Derive version from git tags ([PR #419](https://github.com/hamcrest/JavaHamcrest/pull/419))
 
 ### Bugfixes