docs: clarify frozen results workflow

[Asmit-08]

Summary

• Clarify that new audits and reruns should update results/ without modifying the frozen paper snapshot.
• Document when scripts/freeze_paper_results.py should be used and warn that it replaces the existing snapshot.
• Keep CONTRIBUTING.md and README.md consistent on the frozen-results workflow.

Closes #1071

[vercel]

@Asmit-08 is attempting to deploy a commit to the yashkewlani2020-gmailcom's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

Hey @Asmit-08, your first PR on Fair Code, that's awesome, thank you.

This project is about making AI more accountable, and contributions like yours are what keep that work going. We'll review your changes shortly.

If you haven't already, give the contributing guide a quick read: it covers how audits are structured and what we look for in a review.

And if you're finding Fair Code useful or interesting, a star on the repo genuinely helps more people find it - no pressure, just appreciated.

[github-actions]

@yakew7 @Shreyash0712 - new PR touching a path you own, please review.