Docker image defaults to loading ssl cert/key from environment variables

For configuration of n-s-s, the readme file specifies

CLI flags take precedence over Environment variables, which take precedence over entries in the config file.

I see that the Dockerfile uses environment variables to specify the ssl cert and key:
https://github.com/solid/node-solid-server/blob/ca5bffbf2299a334eb6c5b7d26b37458df8f6624/docker-image/src/Dockerfile#L23-L24

This caused me some confusion when I first tried to configure the cert and key using the config file. It continued to use the values from the env variables over my config file. I was able to override this with a flag.

I think it'd be a good idea to indicate in the docker section of the readme that these environment variables are set, and that if you want to override them you must use the flag rather than the config file.

I initially had a large draft ticket written for this problem, until I found the Dockerfile environment variable and looked at the documentation again and found the section about precedence. I thought I was going crazy because it was loading some values from the config file but not others. I wonder if it could be made clearer, either in debug output, or the documentation about this precedence (for example during debug the server could output something like 'using config setting x from [cli|env|config]'

Thanks!

Start with the Docker section of the README and compare it with the environment variable definitions in docker-image/src/Dockerfile at lines 23–24. Document that these variables are set by the image and that CLI flags are required to override them instead of config-file values. No test is mentioned; done means the Docker configuration and precedence behavior are clear to readers.