FAQ != site usage guidelines. I’m speaking of a topic-specific FAQ to close duplicates on that specific topic. Example of what I mean from SO, C programming tag:
https://stackoverflow.com/tags/c/info (scroll down to “FAQ”)
This one is entirely user-created and maintained. The site itself provides no mechanism for it so we had to show everything into the tag wiki, which is hard to find. New users certainly won’t find it - this is mostly for user moderators who need a list of dupes to close down duplicates with.