Update getting-started.md (#42353)

Clarify that Next.js 13 can be used with the `pages` directory and that `app` features are in Beta. Link to beta docs.

Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>

docs/getting-started.md

@@ -2,7 +2,7 @@
 description: Get started with Next.js in the official documentation, and learn more about all our features!
 ---
 
-> Next.js 13 has been [publicly released](https://nextjs.org/blog/next-13), [read the docs here](https://beta.nextjs.org/docs).
+> Next.js 13 was recently released, [learn more](https://nextjs.org/blog/next-13) and see the [upgrade guide](https://nextjs.org/docs/upgrading#upgrading-from-12-to-13). Version 13 also introduces beta features like the [`app` directory](https://beta.nextjs.org/docs/app-directory-roadmap) that works alongside the `pages` directory (stable) for incremental adoption. You can continue using `pages` in Next.js 13, but if you want to try the new `app` features, [see the new beta docs](https://beta.nextjs.org/docs).
 
 # Getting Started