Add Dockerfile

[szobov]

Rationale

Since the installation requires many actions on the user side, it is better to provide a more convenient and reproducible way to prepare the working environment.

In this case, Docker can mount a directory with the code and have a bidirectional connection to the container.

Implementation

I just used all the commands from README and put them into Dockerfile.
Tested it with:

docker exec -ti gatery /bin/bash -c "cd ~/Documents/gatery/hello_world && make"

Next steps

Use Dockerfile on CI