Added launchd support instead of cron

I added a launchd plist file to control it runnning once a day.

net.belaire.nasa_apod_desktop.plist

@@ -0,0 +1,34 @@
+<?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>net.belaire.nasa_apod_desktop</string>
+
+  <key>ProgramArguments</key>
+  <array>
+    <string>/Users/theobelaire/github/nasa-apod-desktop/nasa_apod_desktop.py</string>
+  </array>
+
+  <key>Debug</key>
+    <true/>
+
+  <key>Nice</key>
+  <integer>1</integer>
+
+  <key>StartCalendarInterval</key>
+  <dict>
+      <key>Hour</key>
+      <integer>6</integer>
+  </dict>
+
+  <key>RunAtLoad</key>
+  <true/>
+
+  <key>StandardErrorPath</key>
+  <string>/tmp/nasa_apod.err</string>
+
+  <key>StandardOutPath</key>
+  <string>/tmp/nasa_apod.out</string>
+</dict>
+</plist>