CONTRIBUTING.md Out of date and has incorrect instructions

[mredig]

New Issue Checklist

• [x] I searched for existing GitHub issues

Describe the bug

I'm not super up to date on the project, but when I updated my PR to use the latest from main, I got the error that ConfigurationProviderRule, which I had conformed my object to, wasn't found. I searched to project to see if it was a build error and the only other spot it was found was in CONTRIBUTING.md.

I spent a few minutes looking through the git history and saw that, apparently, all Rules are now configurable? I haven't had much time to look into it and I don't know what the expected course of action is now, but I can at least take away that CONTRIBUTING.md is out of date and need to be updated by someone who knows what the current expectations are.

P.S. I've gotten my PR to build and pass tests, but I cannot say whether I'm following best practices without a little documentation.