Correct description of -n/--numeric option

Correct description of -n/--numeric option

"When used twice" was used twice in the manpage. :)

And as Florian Westphal pointed out, it was also incorrect
for the -nn case.

Update the manpage and built-in help in main.c to match actual behavior.

Signed-off-by: Jon Jensen <jon@endpoint.com>
Signed-off-by: Florian Westphal <fw@strlen.de>