http://keepachangelog.com/ but for CONTRIBUTING.md
The focus of this project is CONTRIBUTING.md, which is a template that you can use for your own projects. I looked at the most starred projects on Github to collect ideas for this template.
The terrific Keep a CHANGELOG movement is the primary inspiration.
If you don't already have a CONTRIBUTING.md file in your project, then just copy the one from this project. Delete the lines that don't apply, and customise anything that remains.
If you think I'm missing something that could benefit others, then feel free to submit a Pull Request or otherwise suggest modifications and additions.
I have a growing number of projects, some lacking a contributors' guide, and with a great deal of inconsistency and incompleteness amongst the guides that do exist.
I wanted to start a template for my own use that could grow as my projects diversified in teams, programming languages, and approaches.