update change log

Author: beachdweller

CHANGELOG.md

@@ -8,6 +8,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Added the ability to specify the Gemini model when using the AI Tutor GitHub Action.  A new `model` input has been added to the action, allowing users to select different Gemini models.  The default model remains `gemini-1.5-flash-latest` for backward compatibility.
+
 
 ### Changed