c/cruft.pm: Typo fix of a comment

Signed-off-by: Niels Thykier <niels@thykier.net>
README: Link to lintian.d.o for the API docs

They are easier to consume for new users (which would otherwise have
to compile them first).  The downside is that the on-line API is not
necessarily in sync with the API in master branch, so include a note
about that as well.

Signed-off-by: Niels Thykier <niels@thykier.net>