Personally I would edit them on my (up to date) tiddlywiki, export in .tid and drag&drop over the forked github branch. Then fill up the PR, review the changes and edit the files on github if needed.
There is also the custom tiddlywiki edition by saqimtiaz, I dont know if it can still be used but the idea behind it is great : Edit documentation in TW and use Github API to create PRs directly?