docs: add page on contributing through GitHub PRs

[richadr]

Closes #3233

Preview link

[changeset-bot]

⚠️ No Changeset found

Latest commit: dab0b7b

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 GitHub.

Project	Deployment	Review	Updated (UTC)
documentatie	Ready	Preview, Comment	Dec 19, 2025 3:55pm

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Yolijn]

Ik denk dat we ook in CONTRIBUTING bestanden kunnen verwijzen naar deze docs, want ik kwam bijvoorbeeld in Candidate tegen dat we daar juist aanraden om een fork te maken. https://github.com/nl-design-system/candidate/blob/main/CONTRIBUTING.md