When trying to use configuration files, I have been majorly confused about the command line parameters -c and -config. It seems to me that -c is for including commands to your diagrams, and -config is the same, but the commands are in a configuration file.
However, I am not sure about this, and calling `plantuml -h` does not explain anything about it. I do not find much on
https://plantuml.com/faq either.
So as a feature request, please add -c and -config to the help output!