we use discourse for this, which allows wiki posts (post that anyone can edit)
so you can create topics you would like for the 'user guide', and place directly in:
(if not, the I can move them there)
THEN, I can change their type to 'wiki' posts, so that any users can edit.
(you can also edit existing ones, so feel free to do this... again if you dont have permissions let me know)
there is virtually no difference to this and using wiki, with the added bonus that its all in one place, and users searching on the forum will find 'user guide topics too. .. and of course discourse has many functions, including tags etc.
currently, Ive seen no evidence that it the 'technology' (using discourse) thats preventing users contributing to the manual... it just seems that the community has little desire to actually contribute content.
( so personally, I'm not willing to change tech, as i don't believe it will solve the underlying issue - of course others are at liberty to create a wiki if they so desire)