📝 Documentation: Add quick guide to making a new benchmark

[JoshuaKGoldberg]

Bug Report Checklist

• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

I posted a link to this repo in typescript-eslint/typescript-eslint#11241 (comment) as a potential starting base for perf comparisons. Then I realized - it's not really clear how to do that. The docs in this repo are sparse and don't mention how to set up a new comparison. Proposal: let's add those docs in?

Additional Info

No response