Let the user know it's on the `stack` target

Since curl is running quietly it may give the impression that the installation hanged with the last message on the terminal being: "sleep 2 # give docker a moment i guess". In my case I thought it gave it a huge moment and not 2 seconds. It wasn't until the third time that I actually checked the processes on the machine and saw there it was curl downloading stuff quietly.
Merge pull request #723 from ghostbar/patch-1

Let the user know it's on the `stack` target