Definitely separate wiki pages, not Discourse posts converted to Wiki format. A forum such as this is not the place for documentation that is meant to last, and to be easily searched and navigated..
Documentation - which doesn’t change very often - should should have it’s own place where it doesn’t get swamped by the traffic that you get in the Forum.
For example, look at /e/OS. They have their community forum (with thousands of posts, many of them either out-of-date, or just wrong) and completely separate Documentation pages, including the ‘Support Topics’ page with FAQs, How-tos, Devoce-specific guides, and Tips.
Or for another example, look at LineageOS for microG
Support and discussion is in the XDA Forum thread (which is far from ideal - too long, not searchable, not owned by the current maintainers - but it just about does the job), and documentation is in the various wiki pages: for the project and for the Docker image.
For both of those projects, if people are looking for information (rather than discussion, or asking a question) they can be guided to the relevant documentation page(s) (web, wiki, whatever) not told to search hundreds of pages of forum posts.
Most serious, well-resourced FOSS projects have separate documentation pages or sites. And the successful ones that I remember seem to be community-maintained wiki pages, with maybe some form of moderation.
But of course none of this comes for free. Doing documentation properly has a cost - often a significant cost. And it is one of those things that it is easy to ignore, at lease unti the point when you realise that your project really needs some, but doesn’t have any 
</rant>