These files will be copied to the target live ISO via the CoreOS Assembler buildextend-live call. It picks up all files in the coreos/fedora-coreos-config/live/ directory and copies them to the base of the ISO.
Files currently copied are:
- isolinux/boot.msg
- isolinux/isolinux.cfg
Files that get copied into efiboot.img in the ISO:
- EFI/grub.cfg