Improve README: header, badges, quickstart, and repo cross-links

[mishanefedov]

Summary

• Restructured the README with a centered header, badges, and in-page navigation
• Added a quickstart and a star-history chart
• Added a short section linking the other Unison Labs repositories

Test plan

• README renders correctly on GitHub
• Install and usage commands unchanged

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Summary by cubic

Revamps the README with a centered header, clear quickstart, and better navigation to make the SDK easier to install and use. Adds repo cross-links and a star history chart to improve discovery.

• New Features
  • Centered header with logo, tagline, and badges (CI, PyPI, Python, MIT, stars)
  • In-page nav links for Installation, Quickstart, API Reference, Contributing
  • Quickstart moved up and simplified; clarified Python 3.9+ and pip install unisonlabs
  • Renamed “Resources” to “API Reference” and tightened copy
  • Added star history chart
  • Added “Unison Labs constellation” section linking related repos

^{Written for commit ce6bc73. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 1 file

_{Re-trigger cubic}