Iteration on What is Rerun? page

[nikolausWest]

A pass on the "What is Rerun?" page to both simplify it a bit, explain a bit more and make it blueprint aware. I think it might be a good idea to actually explain a little about how it works under the hood as well but will leave that for a separate PR and do it if I have time.

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using newly built examples: rerun.io/viewer
  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!

• PR Build Summary
• Recent benchmark results
• Wasm size tracking

[github-actions]

Deployed docs

Commit	Link
f2277a7	https://landing-omjop6s3z-rerun.vercel.app/docs