Add function to check for installed program

Notifies if program is missing.

.local/bin/ifinstalled

@@ -0,0 +1,4 @@
+#!/usr/bin/env sh
+# If $1 command is not available, error code and notify.
+
+command -v "$1" >/dev/null || { notify-send "📦 $1" "must be installed for this function." && exit 1 ;}