You should mention in README that BaseSystem files in com.apple.recovery.boot MUST be together with the EFI foder in the efi partition. For that partition the disk (usb stick) with a 600 MiB or more space (on a linux machine with gdisk for instance) and an additional partition of at least 30 GiB. The second partition has to be partioned with apfs (very importatnt).
You should mention in README that BaseSystem files in com.apple.recovery.boot MUST be together with the EFI foder in the efi partition. For that partition the disk (usb stick) with a 600 MiB or more space (on a linux machine with gdisk for instance) and an additional partition of at least 30 GiB. The second partition has to be partioned with apfs (very importatnt).