I have written a short and high level tutorial on how to contribute to tiddlywiki documentation. Since TW5 is slightly different from your usual git projects, I thought some clarification is necessary.
This is intended for those who
1. Intend to make sweeping changes in documentation for which browser is not exactly the best medium.
2. Prefers to work on their IDE.
Pre requisites
Familiarity with git and GitHub.
Sincerely,
Riz