contrib: add Mac OS X support files

launchd plist files for chronyd and logrotation.
shell script for logrotation
README file with detailed installation instructions

contrib/bryan_christianson_1/chronylogrotate.sh

@@ -0,0 +1,45 @@
+#!/bin/sh
+
+#  chronylogrotate.sh
+#  ChronyControl
+#
+#  Created by Bryan Christianson on 12/07/15.
+#
+
+LOGDIR=/var/log/chrony
+
+if [ ! -e "$LOGDIR" ]; then
+  echo "missing directory: $LOGDIR"
+  exit 1
+fi
+
+cd $LOGDIR
+
+rotate () {
+  prefix=$1
+
+  rm -f $prefix.log.10
+
+  for (( count=9; count>= 0; count-- ))
+  do
+    next=$(( $count+1 ))
+    if [ -f $prefix.log.$count ]; then
+      mv $prefix.log.$count $prefix.log.$next
+    fi
+  done
+
+  if [ -f $prefix.log ]; then
+    mv $prefix.log $prefix.log.0
+  fi
+}
+
+rotate measurements
+rotate statistics
+rotate tracking
+
+#
+# signal chronyd via chronyc
+
+/usr/local/bin/chronyc -a -f /etc/chrony.d/chrony.conf cyclelogs > /dev/null
+
+exit $?