[add] : Added plank autostart

Author: Hayao0819

channels/xfce/airootfs.any/etc/skel/.config/autostart/Plank.desktop

@@ -0,0 +1,13 @@
+[Desktop Entry]
+Encoding=UTF-8
+Version=0.9.4
+Type=Application
+Name=Plank
+Comment=Elegant, simple, clean dock
+Exec=/usr/bin/plank
+RunHook=0
+StartupNotify=false
+Terminal=false
+Hidden=false
+GenericName=Start Plank dock launcher
+Icon=dock