Add docker image

[tmaier]

This is my try to add a docker image. This would close #262.

The image works, but there are some things not perfect and I am happy for suggestions/contributions.

• The image built gets the label based on the name of the branch. In our case, master
• We should have a latest label
• We should have the ability to build each official release, with release version as label
• It currently builds based on the npm package, not directly the source code of the repository. This means one must update CRITICAL_VERSION in Dockerfile after each release
• Update of README is missing

If you are looking at this, just to find a working and recent docker image, see https://github.com/tmaier/critical/pkgs/container/critical

[bezoerb]

Can anyone with Docker experience take a look at this please?

[tmaier]

Hi @bezoerb, is there anything I can do to get this merged? I would like to stop having a fork, even so it is trivial for me at that point.