as a chronic documentation reader, the best advice i can give is to document everything Anything that the user can and will potentially interact with, should be extensively documented, including syntax and behavior. Write it like you're coming back to the project in 5 years after having done nothing and you want to be able to skip right to using it. When we build something ourselves, we often hold a bit of internal knowledge from the design process that never quite goes away, so it's almost always a lot easier for us to reverse engineer something we've made, than it is for someone else with zero fore-knowledge to do it themselves.

Generally this can be a bit of a nightmare, but if you minimize the user facing segment it's not all that bad, because it's usually pretty minimal, and what would otherwise be a handful of pages, turns into 10 or maybe 15.

as for existing documentation, the i3wm user guide is really good, it's pretty minimalist but it leaves you enough to be able to manage.