Here's the scenario: you have an ageing laptop, the internal NIC has suddenly stopped working, but you don't want to give up here. You uninstall Arch Linux and install Windows 10 just to check that the NIC is actually not functioning anymore (it's not; never do this). You buy a USB Wi-Fi NIC, foolishly not checking if it has Linux support. You boot into an Arch Linux ISO and you don't have an internet connection. Here's what you do next.