Writing custom analyzer docker image


I am investigating custom analyzers and inspect the gitlab provided docker images. I try to use the luacheck Docker image from here: https://github.com/SGTGunner/luacheck-docker/blob/master/Dockerfile

To run this image, one have to mount the current folder into the container /lua path so that luacheck inside the container sees the source files.
docker run -it --rm -v $(pwd):/lua luacheck:v1
I do not currently understand how the gitlab analyzer containers handle that. Also, where the output is piped to, is it stout?

So how could I adapt the Dockerfile to respect the gitlab interfaces regarding file location and output?