A CONTRIBUTING file tells your audience how to participate in your project. For example, you might include information on:
How to file a bug report (try using issue and pull request templates)
How to suggest a new feature
How to set up your environment and run tests
In addition to technical details, a CONTRIBUTING file is an opportunity to communicate your expectations for contributions, such as:
The types of contributions you’re looking for
Your roadmap or vision for the project
How contributors should (or should not) get in touch with you
From open source guides: