Add documentation and package.json metadata for optional react-server-dom-webpack

- Add peerDependenciesMeta to mark react-server-dom-webpack as optional
- Add documentation section explaining the dynamic resolution feature

Co-authored-by: hi-ogawa <[email protected]>

Author: Copilot

packages/plugin-rsc/README.md

@@ -386,6 +386,16 @@ export default defineConfig({
 
 ## RSC runtime (react-server-dom) API
 
+> **Note**: By default, `@vitejs/plugin-rsc` includes a vendored version of `react-server-dom-webpack`. However, if you have `react-server-dom-webpack` installed in your project's dependencies, the plugin will automatically use your version instead. This allows you to stay up-to-date with the latest React Server Components runtime without waiting for plugin updates.
+>
+> To use your own version, simply install it:
+>
+> ```bash
+> npm install react-server-dom-webpack
+> # or
+> pnpm add react-server-dom-webpack
+> ```
+
 ### `@vitejs/plugin-rsc/rsc`
 
 This module re-exports RSC runtime API provided by `react-server-dom/server.edge` and `react-server-dom/client.edge` such as:

packages/plugin-rsc/package.json

@@ -68,5 +68,10 @@
     "react": "*",
     "react-dom": "*",
     "vite": "*"
+  },
+  "peerDependenciesMeta": {
+    "react-server-dom-webpack": {
+      "optional": true
+    }
   }
 }