One question?! We need to support wordpress installations?!
Tell him the exact location of the manual
If the questions keep coming, ask him to send you an email from your profile page. This moves the conversation out of the comments section, which is good because 100 “how do I” comments from the same customer looks bad for poemtial customers and isn’t helpful to buyers looking for legitimate help in the comments either.
Then I’d probably just keep answering basic questions through email, and if anything gets too complex, just say, “this falls outside of the scope of what I provide for free support, but I could help you out on a freelance basis if you like” (or suggest freelance-switch if you don’t take on freelance). But if you do take on freelane, this is one of those situations that could turn into a nice freelance gig so definately keep the communication open and friendly.