Isn’t it easier to just install Libreboot instead?
Depends. If you want to build it from source you get to fight with their build system, which seems to be made with debian (and thus a slightly older GCC) in mind. The big benefit is IMO their payload building which might be closer to what you want than only GRUB or only SeaBIOS with less effort spent. And then there’s stuff they include that you might not want: GRUB background images, a preconfigured setup for GRUB, which might break easily depending on what you use as an OS, etc. Essentially, libreboot is more than just coreboot.
The author also mentions that said GRUB setup fails to boot his OpenBSD installation, so to use Libreboot, you have to get through most of the same steps anyway.
Also, Libreboot doesn’t work well with *BSD. E.g. you cannot use full-disk encryption without serious modifications.
I made a how-to at https://lists.gnu.org/archive/html/libreboot/2016-09/msg00010.html , but it’s easier to just install Coreboot.