Update examples

examples/linux-desktop-notifications/notify-desktop.sh

@@ -2,6 +2,8 @@
 # This is an example shell script showing how to consume a ntfy.sh topic using
 # a simple script. The notify-send command sends any arriving message as a desktop notification.
 
+TOPIC_URL=ntfy.sh/mytopic
+
 while read msg; do
   [ -n "$msg" ] && notify-send "$msg"
-done < <(stdbuf -i0 -o0 curl -s ntfy.sh/mytopic/raw)
+done < <(stdbuf -i0 -o0 curl -s $TOPIC_URL/raw)