The documentation is a community effort, and everyone is welcome to contribute. There is currently already an effort underway to migrate the documentation to “Read the Docs” (RtD), which looks similar to the documentation you linked. You can read more about that effort here:
https://groups.google.com/g/qubes-devel/c/ASj7tehn1G0
You can read more about how to submit documentation changes here:
You may also be interested in the documentation style guide: