This might be an edge case, so feel free to reject the idea.
Currently when entering the boot menu on a Mac to install Arch, the
correct entry to select has a generic usb harddrive logo and the label
"Windows". I don't find this hugely helpful.
If we install the attached icon as '.VolumeIcon.icns' on the EFI
System Partition on the install media we get a nice Arch logo rather
than the generic one.
Changing the label from "Windows" to "Arch Linux Install" (or
something like that), is left for future work. I'll look into that if
unless there are objections to the icon.