This document should contain all information needed by anyway who wishes to contribute to the project.
So it should describe (or link to other documentation files in the package that describe):

• The procedure for submitting (and following up on) a bug report
• The code formatting and naming conventions
• Policy on use of inclusive language, see: T105
• The procedures for submitting code contributions for review
• How such code reviews should proceed (from both reviewer and reviewee perspective)