Keystone is a x86_64 kernel, trying to be compatible with Linux binaries, as it's planning to use musl (a libc).
This doesn't come with Limine binaries, so you need to get them:
make limine
This will get the limine binaries (from v9.x-binary) and copy them to the needed directories.
Then you can build the kernel:
make
This will build the kernel in the bin directory.
You need to also make the Limine ISO, which can be later be put on a USB stick:
make iso
With QEMU:
make qemu
You can customize the QEMU command by editing the qemucmd variable in the GNUmakefile.
Contributions are welcome! If you have any ideas, feel free to open an issue or a pull request.