The entry configuration files understand the following keywords:
title text to show in the menu
version version string to append to the title when the title is not unique
machine-id machine identifier to append to the title when the title is not unique
efi executable EFI image
options options to pass to the EFI image / kernel command line
linux linux kernel image (gummiboot still requires the kernel to have an EFI stub)
initrd initramfs image (gummiboot just adds this as option initrd=)
splash BMP image file to show during bootup
"""
Regards.