Advice users to move to genai-sdk.

Author: pamorgan

README.md

@@ -8,6 +8,8 @@ The Gemini API docs are fully updated to show examples of the new Google Gen AI
 
 Thank you for building with Gemini and [let us know](https://discuss.ai.google.dev/c/gemini-api/4) if you need any help!
 
+**Please be advised that this repository is now considered legacy.** For the latest features, performance improvements, and active development, we strongly recommend migrating to the official **[Google Generative AI SDK for JavaScript](https://github.com/googleapis/js-genai)**.
+
 **Support Plan for this Repository:**
 
 *   **Limited Maintenance:** Development is now restricted to **critical bug fixes only**. No new features will be added.