chore: update example dev script (#41904)

The README and install step already indicates that this example is using Turbopack, which doesn't fully support Tailwind so why not preconfigure the correct dev script from the start?

_(I've left the following checkboxes clear as I do not believe they apply here.)_



## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)


Co-authored-by: JJ Kasper <[email protected]>

examples/with-turbopack/package.json

@@ -2,6 +2,7 @@
   "private": true,
   "scripts": {
     "dev": "next dev --turbo",
+    "dev:tailwind": "concurrently 'next dev --turbo' 'npm run tailwind --watch'",
     "build": "next build",
     "start": "next start",
     "lint": "next lint",