docs: Update README note pointer to the new TS SDK (#447)

Author: Annhiluc

README.md

@@ -1,6 +1,6 @@
 # Google AI SDK for JavaScript
 
-> [!NOTE] A new Javascript/Typescript SDK, `google-genai`
+> [!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.