Add CLI command printing user paths

[hrkfdn]

Describe the solution you'd like

A final thought about this PR would be that it could be interesting to provide a CLI command to obtain all the used paths (cache, config, runtime...). Some other programs do that as well, and it would make the documentation nicer. It could just say 'run ncspot paths' or include it in the help command or something like that, instead of explaining where to look for all the directories. It tells users where the directory is, and not where it might be, which is just a better user experience.

Additional context

From @ThomasFrans in #1313