Gardening in github.com/snapcore/core-build

it would also be nice if someone could merge the four PRs that sit at https://github.com/snapcore/core-build/pulls (i would but i still dont have permissions)

i want to prepare the initramfs-tools-ubuntu-core merge into an initrd/ subdir and would prefer if the new README.md is already in place before, so i can just add to it without conflicts.