I find it's pretty easy to put a link in a comment to the on-topic help page and possibly a related meta post (or canonical question, such as for the licensing questions).
A great deal of these off topic questions are covered by the bold text near the top of that page. If someone can't even be bothered to read that far (or click on the help link in the first place), I'm not sure another help page that is more concise will help them.
That said, people are known to skip FAQ pages with alarming regularity no matter how easy you make it.
It would probably be a better strategy to use javascript to shove the on-topic help page in people's face gently introduce people to the purpose of this site the first time they try to post a question. An abbreviated version of it might be suitable for that purpose.