[sh] Add wording argument to exist script

Added optional third argument to exist script which can be used to
identify the program or process that needs the command exist looks for.
This makes it easier to identify *who* called exist and is missing
something.

sh/.local/bin/exist

@@ -8,9 +8,9 @@ if command -v "$1" >/dev/null; then
 else
   if [ -n "$2" ]; then
     if command -v notify-send >/dev/null; then
-      notify-send "📦 $1" --urgency="$2" "must be installed for this function."
+      notify-send "📦 $1" --urgency="$2" "must be installed for ${3:-"this"} function."
     fi
-    printf "%s: 📦 %s must be installed for this function.\n" "$2" "$1"
+    printf "%s: 📦 %s must be installed for %s function.\n" "$2" "$1" "${3:-"this"}"
   fi
   exit 1
 fi