There is content here for both users of Open Brush and for people that want to contribute to its development.
It's currently a massive work in progress and various links and info will be incorrect but we're just trying to get all the information currently available in one place.
Writing good docs takes time. We'd love people to help. Hop on our Discord or just write some docs and let us know about them. There's a bunch of you out there who know more about actually using Open Brush than we as developers do and your contribution would be invaluable.