cclib CI Docker images

Building the images:

1. cd path to py3*
2. sudo docker buildx build -t shivupa/cclib-ci:py37 . | tee buildlog.txt
3. sudo docker image ls (get the build hash of the latest image
4. sudo docker tag BUILDHASH shivupa/cclib-ci:py37
5. sudo docker push shivupa/cclib-ci:py37

You may need to install https://github.com/docker/buildx first.

Your .secrets file (in .env format, just like setting a local variable in a sh shell script) must contain GITHUB_TOKEN for the Docker metadata action to work. It is a personal access token that only needs repository read permissions to work. If using a "fine-grained" token, no additional permissions beyond the defaults are necessary.