docs: note about v3 release (#8171)

README.md

@@ -33,9 +33,18 @@ In addition, Vite is highly extensible via its [Plugin API](https://vitejs.dev/g
 
 [Read the Docs to Learn More](https://vitejs.dev).
 
-## Packages
+## v3.0
+
+Current Status: **Alpha** (for internal testing, not recommended for production)
+
+The `main` branch is now for v3.0, if you are looking for current stable releases, check the [`v2` branch](https://github.com/vitejs/vite/tree/v2) branch instead.
 
-> This branch is for the upcoming v3.0, if you are looking for current stable releases, check the [`v2` branch](https://github.com/vitejs/vite/tree/v2) instead.
+We will start drafting release notes and migration guide for v3.0 when we enter the beta stage. Before that you can check:
+
+- [v3.0 Milestone](https://github.com/vitejs/vite/milestone/5)
+- [Breaking Change List](https://github.com/vitejs/vite/issues?q=label%3A%22breaking+change%22+is%3Aclosed+milestone%3A3.0)
+
+## Packages
 
 | Package                                           | Version (click for changelogs)                                                                                                       |
 | ------------------------------------------------- | :----------------------------------------------------------------------------------------------------------------------------------- |