The page you are reading is part of a draft (v2.0) of the "No bullshit guide to math and physics."
The text has since gone through many edits and is now available in print and electronic format. The current edition of the book is v4.0, which is a substantial improvement in terms of content and language (I hired a professional editor) from the draft version.
I'm leaving the old wiki content up for the time being, but I highly engourage you to check out the finished book. You can check out an extended preview here (PDF, 106 pages, 5MB).
git remote add upstream <git repository you want to contribute to> git remote update
git checkout -b upstream upstream/master git cherry-pick <SHA1 hash of bugfix commit> git cherry-pick <SHA1 hash of another commit to add> git push origin upstream
and then I see my upstream branch on github, switch to it and can submit the pull request with just the changes I want.