update readme with link to new preview-launch js-genai sdk repo

Author: imperorrp

README.md

@@ -1,5 +1,8 @@
 # Google AI SDK for JavaScript
 
+> [!NOTE]
+> A new Javascript/Typescript SDK, `google-genai` ([github](https://github.com/googleapis/js-genai/tree/main)), is currently available in a *preview launch*- designed to work with Gemini 2.0 features and support both the Gemini API and the Vertex API. 
+
 The Google AI JavaScript SDK is the easiest way for JavaScript developers to
 build with the Gemini API. The Gemini API gives you access to Gemini
 [models](https://ai.google.dev/models/gemini) created by