The first thing that came to mind when I read "Wouldn’t it be convenient if the documentation... already had an answer for someone with the same problem?" was "Oh, like the comments on the PHP docs?"

It's a clunky mechanism and there's years' worth of cruft in there, but interspersed with years' worth of knowledge, and I've often wished other languages had a similar canonical repository of user-contributed information. I seldom touch PHP at the moment, but reflecting on how many times I found a quick solution to something simply by perusing the comments on a function's page makes me think this approach could have huge potential if implemented in a more elegant way.