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/org.tuxfamily.chronyc.plist

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>Label</key>
+	<string>org.tuxfamily.logrotate</string>
+	<key>KeepAlive</key>
+	<false/>
+	<key>ProgramArguments</key>
+	<array>
+		<string>/bin/sh</string>
+		<string>/usr/local/bin/chronylogrotate.sh</string>
+	</array>
+	<key>StartCalendarInterval</key>
+	<dict>
+		<key>Minute</key>
+		<integer>5</integer>
+		<key>Hour</key>
+		<integer>4</integer>
+	</dict>
+</dict>
+</plist>