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!

从 README 的 Docker 部分开始，并将其与 docker-image/src/Dockerfile 第 23–24 行中的环境变量定义进行比较。记录这些变量由镜像设置，并且需要使用 CLI flags 而不是配置文件中的值来覆盖它们。没有提到测试；完成的标准是 Docker 配置和优先级行为对读者来说清晰明确。