Goal: dynamically build rootfs from packages stored outside of initramfs
Status: success

as POC I'm running sl (steam locomotive) as init after changing root

for this experiment I needed to compile linux kernel with overlayfs, virtio and
9p drivers built in. Alternatively I could compile kernel with ext4 support and
load modules

- new dir "pkgs.sl" contains packages required for steam locomotive to run
- make now creates pkg_store that contains unpacked packages from pkgs.sl
- run_qemu.sh now also adds virtio 9p mount with pkg_store
- init script mounts pkg_store and builds rootfs from it (and initramfs as base
  system)