mdmon: Add missing option documentation to --help output

Document that -a is equivalent to --all, as well as --foreground / -F

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.de>

mdmon.c

@@ -271,7 +271,8 @@ void usage(void)
 "\n"
 "Options are:\n"
 "  --help        -h   : This message\n"
-"  --all              : All devices\n"
+"  --all         -a   : All devices\n"
+"  --foreground  -F   : Run in foreground (do not fork)\n"
 "  --takeover    -t   : Takeover container\n"
 );
 	exit(2);