We recently added support for multi-architecture Docker images using

docker buildx. This requires a bit of additional setup to build one or

more buildkit environments. While not hard (especially if running on

macOS, which can build arm64 and amd64 images), it's non-obvious how to

build these if you haven't done it before.
For more advanced setups where multiple hosts are involved in the build

process, it's especially non-obvious, and not even the docker buildx

instructions cover this well. And just using docker buildx means that

there's more complexity involved in testing and using these images.
The top of the Dockerfile now has instructions on setting up buildx

for both single-host and multi-host builds.
The build.py script has been updated to better support this as well.

It's been given a --platform option for specifying one or more

platforms, and a --load option for taking a single built platform

and loading it into the local Docker for testing.

Followed these instructions and built a multi-host, multi-architecture

build environment, and built new images.
Used --load to get a built image into my local environment.