Introduction to the different ways to get involved with the project. Reporting bugs, suggesting features or changes or by contributing directly with the code. Be sure to define the steps for each different way of contributing.
Section to define where to discuss about the project. It is common to have a forum or using github issues.
Specific steps that contributors should take care before submitting a pull request. It is your choice to include a guide to how to test code changes, code style and other relevant information to your project. Also mention how the team behind the project takes care of the pull requests and the timeframe regarding the pull request.
Section to talk about the difference between authors and contributors. Example (must be included verbatim in all Codeando México repositories):
Authors are contributors that had the original idea and usually responsible for the initial bulk commits.
People who have contributed with code changes, documentation or bug fixes to the project, only by submitting a pull request. They should be ordered by initial contribution date in the CONTRIBUTORS.md file.
Responsible for development and maintenance of the project. In charge of responding to pull requests and leading discussion about the project. In our case, they are usually members of Codeando México.