[racket] show-requires isn't submodule-aware?

I'm actually really curious how it works and tempted to try to fix it
myself, because I expect I would learn so much. What I don't know is
how much learning that would turn out to be, and how long it would
take me. Especially if your intuition is that it might be hard, for
you. :)

In any case I don't think it's an urgent issue.