Are you familiar with Sphinx and Readthedocs ?
That's what we use for writing and generating documentation.
Make sure you have sphinx installed on your local machine and fork and clone our github repository.
Then you can do:
$ cd django-extensions
$ cd docs
$ make clean
$ make html
This will generate the documentation for you locally.
Use your webbrowser of choice to open _build/html/index.html from that directory to view them.
Now you can start writing and updating documentation.
If your not familiar with Sphinx it's probably best to start reading their documentation and tutorial first.
You can send updates to us via Github pull requests or email them to me or ping me on irc (freenode).