Add changelog

Author: Djneu

CHANGELOG.md

@@ -19,6 +19,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Changed
 - The tian2019 composition model now returns a mass fraction instead of a mass percentage. \[Daniel Douglas; 2024-11-12; [#767](https://github.com/GeodynamicWorldBuilder/WorldBuilder/pull/767)\]
 ### Fixed
+- Fixed index for 2D compositional fields in gwb-grid. \[Derek Neuharth; 2025-01-21; [#788](https://github.com/GeodynamicWorldBuilder/WorldBuilder/pull/788)\]
 
 ## [1.0.0]
 ### Added