Document `manualChunks` example

[hi-ogawa]

We already test this in examples/basic and we can document this as basic suggestion.

vite-plugin-react/packages/plugin-rsc/examples/basic/vite.config.ts

Lines 125 to 163 in a96a6b2

	{
	name: 'optimize-chunks',
	apply: 'build',
	config() {
	const resolvePackageSource = (source: string) =>
	normalizePath(fileURLToPath(import.meta.resolve(source)))
	// TODO: this package entry isn't a public API.
	const reactServerDom = resolvePackageSource(
	'@vitejs/plugin-rsc/react/browser',
	)
	return {
	environments: {
	client: {
	build: {
	rollupOptions: {
	output: {
	manualChunks: (id) => {
	// need to use functional form to handle commonjs plugin proxy module
	// e.g. `(id)?commonjs-es-import`
	if (
	id.includes('node_modules/react/') ||
	id.includes('node_modules/react-dom/') ||
	id.includes(reactServerDom)
	) {
	return 'lib-react'
	}
	if (id === '\0vite/preload-helper.js') {
	return 'lib-vite'
	}
	},
	},
	},
	},
	},
	},
	}
	},