Update CHANGELOG.md for v0.3.0

CHANGELOG.md

 # CHANGELOG
 
+## [0.3.0] - 2024-05-27
+
+### Added
+* Add Qmix & PW-OPO-BB support by @NoahDornhecker in https://github.com/BenediktBurger/snlo-helper/pull/3
+* Add license by @BenediktBurger in https://github.com/BenediktBurger/snlo-helper/pull/2
+
+### New Contributors
+* @BenediktBurger made their first contribution in https://github.com/BenediktBurger/snlo-helper/pull/2
+* @NoahDornhecker made their first contribution in https://github.com/BenediktBurger/snlo-helper/pull/3
+
+**Full Changelog**: https://github.com/BenediktBurger/snlo-helper/compare/v0.2.0...v0.3.0
+
+
 ## [0.2.0] - 2024-05-07
 
 _Completely restructured package for easier maintenance and extension._