docs: added --appRouter CLI flag to docs (#2003)

www/src/pages/en/installation.mdx

@@ -58,6 +58,7 @@ For our CI, we have some experimental flags that allow you to scaffold any app w
 | `--nextAuth`              | Include NextAuth.js in the project           |
 | `--tailwind`              | Include Tailwind CSS in the project          |
 | `--dbProvider [provider]` | Include a configured database in the project |
+| `--appRouter`             | Use Next.js App Router in the project        |
 
 <Callout type="warning">
   If you don't provide the `CI` flag, the rest of these flags have no effect.