Add --help command and other quality of life flags for choosing log level etc.

[Decodetalkers]

portal is started by systemd, so the flags maybe need config file, like toml to set

and it is not a cli tool, so I think just write the document is enough?

[Shinyzenith]

Yep a configuration language also works. I'll try implementing this. I don't know what the serde drama is but I'll look into it.