📝(docs) improve readme and add documentation hub

[actuallypav]

Purpose

This pull request improves the project’s documentation entry points and overall readability to make Docs more approachable for new users and contributors.

While reviewing the repository, I noticed that the project highlights documentation and Markdown support, but the front-page README contained several Markdown syntax issues and inconsistencies. This made the landing experience feel less polished than the quality of the project itself. The goal of this change is to provide a cleaner, more consistent, and more professional first impression.

Please let me know and I can apply any changes, or edit other .md files as needed!

Proposal

• Rewrite the root README to be tighter, easier to scan, and more user-facing
• Add a documentation landing page at /docs/README.md with a structured table of contents
• Introduce docs/instances.md to list public Docs instances

External contributions

Thank you for your contribution! 🎉

Please ensure the following items are checked before submitting your pull request:

• I have read and followed the contributing guidelines
• I have read and agreed to the Code of Conduct
• I have signed off my commits with git commit --signoff (DCO compliance)
• I have signed my commits with my SSH or GPG key (git commit -S)
• My commit messages follow the required format: <gitmoji>(type) title description
• I have added a changelog entry under ## [Unreleased] section
• I have not added tests because this PR only contains documentation changes