docs: added polish translation to folder-structure-app.mdx

[wiktrek]

✅ Checklist

• I have followed every step in the contributing guide (updated 2022-10-06).
• The PR title follows the convention we established conventional-commit

---

Changelog

• Added polish translation to folder-structure-app.mdx
• changed link in en/folder-structure-app.mdx to next.js app router docs
• added IntroductionTab component in pl/introduction.mdx
  💯

[changeset-bot]

⚠️ No Changeset found

Latest commit: 8df5464

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
create-t3-app	✅ Ready (Inspect)	Visit Preview	💬 1 unresolved ✅ 1 resolved	Aug 8, 2024 1:39pm

[github-actions]

Hey t3-oss/translators!

This PR contains changes to your language. Please review the changes ❤️.

PL: @matibox, @Infiplaya, @PiotrekPKP

[vercel]

@wiktrek is attempting to deploy a commit to the t3-oss Team on Vercel.

A member of the Team first needs to authorize it.

[juliusmarminge]

This is outdated (sorry for not reviewing) so converting to draft. Ping me on Discord when it's ready