Better docker setup

[EmilieDel]

Fixes #49.

A few ideas for improving our Docker setup.

• [X] Rename the file as Dockerfile or deep_atlas.Dockerfile (w/o the Dockerfile extension, the file format is not recognized)
• [X] Add functionalities to create users and run the Docker image as a non-root user (e.g. see what done in morphoclass here). In general, running Docker images as root is quite dangerous, and allows the creation of files that then are impossible to remove (unless you're root).
• [X] Move all Docker-related files and scripts under a docker/ directory (e.g. see what done in morphoclass here).
• [X] Add instructions on how to use Docker in the README.md (e.g. something like this text).
• [x] Test that docker build and docker run work on Apple M1.

[jankrepl]

For future reference, I was able to build the image on my Macbook M1 with this command

cd docker
DOCKER_BUILDKIT=0 docker build  -f Dockerfile -t deepatlas --platform linux/amd64  .

I mounted the folder with the source code when docker run.

I currently get the following error/warning when full_pipeline.py does interpolation https://discuss.pytorch.org/t/bug-w-nnpack-cpp-80-could-not-initialize-nnpack-reason-unsupported-hardware/107518