depmod: Fix handling relative moduledir

depmod: Fix handling relative moduledir

Make sure moduledir is always relative to the basedir and document it as
such.

Note: scdoc 1.11.3 produces a strange result when trying to render the
man page for the 2 examples. Workaround that by ending with an explicit
newline, which produces another stranger behavior (but visually correct)
of indenting the next line.

Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/243