Enhancement: show the root cause for potential `Could not generate docum...

...entation`

While generating docs for a my-app.core a `Could not
generate documentation` was thrown. The root cause was
not clear at first. Eventually it tracked down to an
unreferenced (but needed by the framework I'm using)
routes.clj not explicitly `:use my-app.xxx` in the `ns`
declaration.

I don't know if this is a common problem, but the general
idea of being able to quickly see the root cause seems to
be an OK one?
Apologies if the format isn't to your liking!