Mention the script should not be executed offline

[iTrooz]

I tried to execute tiny11maker.ps1 on a virtual machine cut off from the network, and after the script finished (Whiwh was just after "Unmounting image"), I found myself without a tiny11.iso file in the folder.

After searching through Internet and this repo's issues and finding nothing, I re-ran the script in an already existing prompt to try to get a better look at potential errors, and I found this:

Might be good to detect whether the network is accessible, and print an error message. Also, to not auto-close the terminal window on error.