In the FAQ, there is a list of concepts that would make a question off-topic. It seems to me like this would be a great place to redirect users to Stack Overflow and Programmers, as what is off-topic for Code Review is probably a good fit for those sites.
The About page cannot be edited thoroughly enough to link to these sites, nor is it really necessary unless the user posts an off-topic question.
The latest close reasons in effect, which were established here, now include links to both Stack Overflow and Programmers. When a question is closed, users will know to post on either of these sites.