Add usage

earth_wallpaper.sh

@@ -37,6 +37,11 @@ check_font() {
   fi
 }
 
+usage() {
+  echo "Usage:"
+  echo "$(basename "${0}") --city <CITY> [--help] [--temperature-unit celsius|fahrenheit] [--wallpaper-file <FILE>] [--archive-folder <FOLDER>] [--screen-width <WIDTH>] [--font-name <FONT_NAME>] [--debug] [--logfile]"
+}
+
 temp_unit=celsius
 wallpaper_file="${HOME}/wallpaper.jpg"
 wallpaper_file2="/etc/lightdm/background.jpg"
@@ -50,6 +55,11 @@ font_name=$("${gsettings_cmd}" get org.gnome.desktop.interface font-name | sed "
 while [ $# -gt 0 ]
 do
   case "$1" in
+    "--help")
+      shift
+      usage
+      exit 0
+      ;;
     "--temperature-unit")
       shift
       temp_unit="${1}"