The document outlines 5 unspoken rules for contributing to open source software: 1) Justify your proposed changes, 2) Be willing to discuss and revise your contributions, 3) Be positive and grateful, 4) Make small, focused changes that are easier to review and accept, and 5) It's often easier to create companion software rather than modify existing code. The document provides examples and explanations for each rule to help new contributors successfully participate in open source projects.