This wiki uses the Markdown syntax.
The wiki itself is a mercurial repository, which means you can clone it, edit it locally/offline, add images or any other file type, and push it back to us. It will be live immediately.
Go ahead and try:
$ hg clone https://firstname.lastname@example.org/drrossum/supernu/wiki
Wiki pages are normal files, with the .md extension. You can edit them locally, as well as creating new ones.