Added ntp

The script that the ntp systemd service executed is a SysVinit script that used PIDs, but due to pid-guessing it's prone to failure by design. See http://smarden.org/runit/benefits.html
The run script of this runit service was altered from that SysVinit script to run in the foreground.
SysVinit scripts are long,verbose, and complex which is a shame, because it scared people from init scripts in general.
Runit scripts are very simple, as they just alter the environment if necessary, before exec'ing into the service.
They rarely take more than a couple lines.

sv/ntp/run

@@ -0,0 +1,19 @@
+#!/bin/sh
+sv start networking
+sv stop systemd-timesyncd
+DAEMON=/usr/sbin/ntpd
+if [ -r /etc/default/ntp ]; then
+        . /etc/default/ntp
+fi
+
+if [ -e /run/ntp.conf.dhcp ]; then
+        NTPD_OPTS="$NTPD_OPTS -c /run/ntp.conf.dhcp"
+fi
+
+RUNASUSER=ntp
+UGID=$(getent passwd $RUNASUSER | cut -f 3,4 -d:) || true
+
+if test "$(uname -s)" = "Linux"; then
+        NTPD_OPTS="$NTPD_OPTS -u $UGID"
+fi
+exec $DAEMON --nofork $NTP_OPTS