grub-bios-setup
Set up a device to use GRUB with a BIOS configuration.
TLDR
Set up a device to boot with GRUB
$ grub-bios-setup [/dev/sdX]
Install even if problems are detected
$ grub-bios-setup --force [/dev/sdX]
Install GRUB in a specific directory
$ grub-bios-setup --directory=[/boot/grub] [/dev/sdX]