To create an initramfs:
1. Edit config to your liking
2. Run ./mkinitramfs
The default config will create a minimal initramfs suitable for a full disk
encryption setup. It'll include the cryptsetup binary, and use it to open the
encrypted drive specified in the crypt_root kernel parameter (same as
genkernel). It'll also include intel microcode for the current running CPU.
This config needs busybox, cryptsetup and iucode_tool installed.