Update CHANGELOG.md for v0.5.0 (#82)

Updating the changelog to match #81

Author: kratman

CHANGELOG.md

@@ -1,3 +1,8 @@
+# [v0.5.0](https://github.com/FaradayInstitution/BPX/releases/tag/v0.5.0)
+
+- Bug fixes for Pydantic ([#81](https://github.com/FaradayInstitution/BPX/pull/81))
+- Updated to Pydantic V2 and the hatch build system ([#79](https://github.com/FaradayInstitution/BPX/pull/79))
+
 # [v0.4.0](https://github.com/FaradayInstitution/BPX/releases/tag/v0.4.0)
 
 - Added five parametrisation examples (two DFN parametrisation examples from About:Energy open-source release, blended electrode definition, user-defined 0th-order hysteresis, and SPM parametrisation). ([#45](https://github.com/FaradayInstitution/BPX/pull/45))