I usually deal with these types of questions by sending them a link to a specific document. For example, I might say, "take a look at the flow diagram at ${url}, then read the notes on ${node}, they will explain why you are getting that error". If the person comes back and says, "I read your notes but I have no idea what they mean", I'd point him to some introductory material; but in practice, this happens rarely, because my notes are full of links.

One thing I used to do, but stopped doing, was to say, "open up the project wiki and read through all the pages in it". The people who come to me with questions are looking for an effective solution to a specific problem, not for general education and/or enlightenment. They have tangible goals just like I do, after all, and there are only so many hours in a day.