How to use IDEA to develop a Docker image?

I understand how to use the docker plugin e.g. in a Java project. What I would like to do is something different: I want to use IDEA to develop and test a Docker image, and/or a multi-container yaml file. There will be additional supporting files, such as a readme.md and maybe some shell scripts.

I can't really find a proper project structure to do this. There is no "Docker" project, so I started with an empty project. This one complains that I do not have a project SDK, which I don't need. I also can't make a module to add the "source" files, because I can't find a module type that would fit (not even a "plain" or "text file" module).

What am I supposed to do? Thanks!