update the example configuration file from upstream

ntpd.conf

@@ -1,3 +1,4 @@
+# $OpenBSD: ntpd.conf,v 1.2 2015/02/10 06:40:08 reyk Exp $
 # sample ntpd configuration file, see ntpd.conf(5)
 
 # Addresses to listen on (ntpd does not listen by default)
@@ -9,4 +10,12 @@
 # use a random selection of NTP Pool Time Servers
 # see http://support.ntp.org/bin/view/Servers/NTPPoolServers
 servers pool.ntp.org
-constraints from "https://www.google.com/search?q=openntpd"
+
+# use a specific local timedelta sensor (radio clock, etc)
+#sensor nmea0
+
+# use all detected timedelta sensors
+#sensor *
+
+# get the time constraint from a well-known HTTPS site
+#constraints from "https://www.google.com/search?q=openntpd"