A data model for Git (and other docs updates)

Julia Evans and Marie Flanagan contributed improvements to Git's official documentation, including a new data model document explaining core concepts like objects, references, and the index. They updated man pages for git add, git checkout, git push, and git pull based on feedback from 80 test readers who identified confusing terminology and unclear explanations. The process involved using GitGitGadget to convert GitHub pull requests into email patches for the Git mailing list, and demonstrated an evidence-based approach to documentation improvement by gathering user feedback rather than relying on expert opinions.