termux-notification: specify -c/stdin precedence

-c/--content takes precedence over stdin to set the notification's
content

Author: xalexalex

scripts/termux-notification

@@ -4,7 +4,7 @@ set -e -u -f
 SCRIPTNAME=termux-notification
 show_usage () {
     echo "Usage: termux-notification [options]"
-    echo "Display a system notification. Content text is read from stdin or specified using --content."
+    echo "Display a system notification. Content text is specified using -c/--content or read from stdin ."
     echo "  --action action          action to execute when pressing the notification"
     echo "  --alert-once             do not alert when the notification is edited"
     echo "  --button1 text           text to show on the first notification button"