You need docker buildx and qemu-user-static and a buildkit builder that is using the docker-container or kubernetes driver if you want to build multi-arch images.

This are the necessary steps to get it working on arch linux

pacman -Sy docker-buildx qemu-user-static
docker buildx create --driver=docker-container --bootstrap --use

Additonally you need to be signed in into the github container registry. A guid for how to do this can be found here.

You can run the build.sh script in two modes. If you run it without any arguments it uses your local git tree including any uncommitted changes to build the docker containers.

If you run ./build.sh git it will do a fresh git checkout of the same commit as you currently on for building.