ntpd: mention in help text that -d can be repeated

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

networking/ntpd.c

@@ -71,7 +71,7 @@
 //usage:	"[-dnqNw"IF_FEATURE_NTPD_SERVER("l -I IFACE")"] [-S PROG] [-p PEER]..."
 //usage:#define ntpd_full_usage "\n\n"
 //usage:       "NTP client/server\n"
-//usage:     "\n	-d	Verbose"
+//usage:     "\n	-d	Verbose (may be repeated)"
 //usage:     "\n	-n	Do not daemonize"
 //usage:     "\n	-q	Quit after clock is set"
 //usage:     "\n	-N	Run at high priority"