document how Octave binary snapshot is built
From this project's point of view, the octave-${OCTAVE_VERSION}-ubuntu-bionic-amd64.tar.gz
file is an opaque binary blob.
I intend to create other projects to make this process completely transparent, automated, and reproducible. This project should at least have some minimal documentation explaining how that binary blob is built and how it integrates into the rest of Dockerfile.