docs: note about monorepo usage

Author: antfu

README.md

@@ -91,6 +91,40 @@ it('exports snapshot', async () => {
 
 [A more complete usage example in Shiki](https://github.com/shikijs/shiki/commit/ece4b02a82febea02349ad200e0d07ab59a6a304)
 
+### Monorepo Usage
+
+Since this utility is only a function, you can compose it freely to fit your monorepo structure.
+
+If you want to snapshot all packages in your pnpm monorepo, here is an example we use in VueUse:
+
+```ts
+import yaml from 'js-yaml'
+import { x } from 'tinyexec'
+import { describe, expect, it } from 'vitest'
+import { getPackageExportsManifest } from 'vitest-package-exports'
+
+describe('exports-snapshot', async () => {
+  const packages: { name: string, path: string, private?: boolean }[] = JSON.parse(
+    await x('pnpm', ['ls', '--only-projects', '-r', '--json']).then(r => r.stdout),
+  )
+
+  for (const pkg of packages) {
+    if (pkg.private)
+      continue
+    it(`${pkg.name}`, async () => {
+      const manifest = await getPackageExportsManifest({
+        importMode: 'src',
+        cwd: pkg.path,
+      })
+      await expect(yaml.dump(manifest.exports, { sortKeys: (a, b) => a.localeCompare(b) }))
+        .toMatchFileSnapshot(`./exports/${pkg.name.split('/').pop()}.yaml`)
+    })
+  }
+})
+```
+
+This will create a file snapshot for each package in the `./exports` directory.
+
 ## How it works
 
 When `getPackageExportsManifest` is called, it will: