another dependency

Bruno Haible <[email protected]> Wed, 01 Feb 2023 19:05:53 +0100

Newsgroups	gmane.comp.printing.a2ps.bugs
Message-ID	<2123892.1Tx1zexCxq@nimes>

On OpenBSD 6.5, the configure output contains this:

checking for grog... no
configure: WARNING: ============================================================
a2ps works better with groff.
Consider fetching groff at any ftp site proposing GNU programs
configure: WARNING: ============================================================

This should also be mentioned as an optional dependency in the DEPENDENCIES
file.