docs: document fallback pages provided by the service

[MikkelHebel]

Summary

Adds a ## Pages section to the README documenting every page this service can serve, what triggers each one, and what it looks like.

• Lists all generated pages with their title and intended use
• Adds screenshots for each page under docs/images/, captured by running generator.py

This closes #6

[github-actions]

All Contributors have signed the CLA. Thank you for your cooperation!
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[MikkelHebel]

I have read the CLA Document and I hereby sign the CLA

[MikkelHebel]

I've also added dark mode screenshots