Docs: Update README

[isabelle-dr]

Added video demo, improved the top section of the document, added links to rule mapping docs

Expected behavior:

Please make sure these boxes are checked before submitting your pull request - thanks!

• [ ] Run the unit tests with gradle test to make sure you didn't break anything
• Format the title like "feat: [new feature short description]". Title must follow the Conventional Commit Specification(https://www.conventionalcommits.org/en/v1.0.0/).
• Linked all relevant issues
• Include screenshot(s) showing how this pull request works and fixes the issue(s)

[github-actions]

Thank you for this contribution! 🍰✨🦄

Information about source corruption

0 out of 1337 sources are corrupted.

Acceptance test details

The changes in this pull request did not trigger any new errors on known GTFS datasets from the MobilityDatabase.
Download the full acceptance test report for commit 05b8f94 here (report will disappear after 90 days).

[maximearmstrong]

LGTM ✨ Thank you @isabelle-dr!

[github-actions]

Thank you for this contribution! 🍰✨🦄

Information about source corruption

0 out of 1337 sources are corrupted.

Acceptance test details

The changes in this pull request did not trigger any new errors on known GTFS datasets from the MobilityDatabase.
Download the full acceptance test report for commit e8836a0 here (report will disappear after 90 days).

[isabelle-dr]

Thank you @maximearmstrong for making this amazing interface!