Update FlareDB runner doc

[ganesh-skumar]

This PR updates the runner doc with:

• New install script: Replaces the default cargo-dist generated script with install.sh, which downloads binaries hosted on Cloudflare R2 and published via this workflow. The previous GitHub-hosted option was slow, rate-limited, and gave a poor first experience.
• Adds a section on checking logs

[ganesh-skumar]

assign set of reviewers

[github-actions]

Assigning reviewers:

R: @kennknowles for label website.
Backup reviewer: Abacn (if the main reviewer is unresponsive, you can escalate to them by tagging their username)

Note: If you would like to opt out of this review, comment assign to next reviewer.

Available commands:

• stop reviewer notifications - opt out of the automated review tooling
• remind me after tests pass - tag the comment author after tests pass
• waiting on author - shift the attention set back to the author (any comment or push by the author will return the attention set to the reviewers)

The PR bot will only process comments in the main thread (not review comments).