Build instructions

[jcarr-awake]

I can't see any instructions for building the project, and the exact barney commands to run might not be obvious without full experience (such as when one is looking to use eext for the first time).

Docker build/run instructions would also be helpful, as a naive docker build . and docker run <sha256> -t /bin/bash froze for me, where sha256 is the name of the docker build result.