There has been a brief discussion on the topic, mostly surrounding using Discourse as an interim.
Website published from the github readme docs + community supported Discourse wiki/how-to posts
I personally feel it should fall within the "official" Joplin sphere, either in the community (i.e. discourse) area or the "official" (i.e. website + github) area.
One of the nice things about having the official docs separated from the community content is that the barrier to entry for the community content is significantly lower (no need for github) and requires less time from repo collaborators to approve any documentation changes. The community content is simply able to be edited by more or less anyone at any time and allows for topics that you don't necessarily want as a front facing document on a website (for example my guide on how to un-delete stuff).