Some add-on workbenches have their own dedicated pages on the FreeCAD wiki. Yorik has stated his wish that all add-ons be documented on the wiki. I think it would be acceptable (and desirable) to have your documentation on the FreeCAD wiki, where it can be translated into other languages.
If you decide to write your documentation on your Github repo, we can probably just copy its content (with minor syntax changes) to the FreeCAD wiki, that is of course, if the license you choose allows it.
Which reminds me that apart from the Release notes 0.17, the Navigation Indicator is not documented anywhere in the wiki... Will put that on my todo list.