Kevin R. Barnes:
We’ve tried making this easy for everyone. As a maintainer, all you have to do is add a CONTRIBUTING file (or CONTRIBUTING.md if you’re using Markdown) to the root of your repository. Then we will add a link to your file when a contributor creates an Issue or opens a Pull Request.
I like GitHub (both as a product and as a company) because they continue to incorporate conventions established by users into their product. Kinda the opposite of Twitter.