docs(fullstack): add discussion link (#1284)

Author: hi-ogawa

packages/fullstack/README.md

@@ -1,3 +1,7 @@
+> [!NOTE]
+> This was a draft version of the prospoal, which is now available on [Vite discussion](https://github.com/vitejs/vite/discussions/20913).
+> Please leave a comment there if you have any feedback.
+
 # Proposal: Client assets metadata API for SSR
 
 This proposal introduces a new API that enables server code to access client runtime assets metadata required for server-side rendering in a framework agnostic way. This feature is currently prototyped in the package [`@hiogawa/vite-plugin-fullstack`](https://github.com/hi-ogawa/vite-plugins/tree/main/packages/fullstack) with [examples](#examples).