Update CHANGELOG.md

Author: daymxn

firebase-ai/CHANGELOG.md

@@ -2,7 +2,8 @@
 * [feature] Initial release of the Firebase AI SDK (`firebase-ai`). This SDK *replaces* the previous
  Vertex AI in Firebase SDK (`firebase-vertexai`) to accommodate the evolving set of supported
  features and services.
-  * The new Firebase AI SDK provides **public preview** support for the Gemini Developer API, including its free tier offering.
+  * The new Firebase AI SDK provides **public preview** support for the
+  [Gemini Developer API](https://ai.google.dev/gemini-api/docs){: .external}, including its free tier offering.
   * Using the Firebase AI SDK with the Vertex AI Gemini API is still generally available (GA).
 * [feature] **Public Preview:** Added support for specifying response modalities in GenerationConfig
  (only available in the new `firebase-ai` package). This includes support for image generation using