concrete5.org now features much improved documentation, both for developers and for end users.

https://www.concretecms.com/documentation/

No more developer docs separated from user docs. Tags also make it easy to cross-reference pages with forum posts that refer to them. Related discussions marked as helpful should also float toward the top on their related docs pages. Much, much more (and sensibly organized) developer content. No more "page coming soon" messages. Search should also be much improved.