CLI / Commands definition

[sfermigier]

We need to write down the list of commands, subcommands and main options that we need for the system to work.

The names use need to be familiar to users to similar tools:

• pip / poetry / pipenv / npm / yarn / gem / ...
• rpm / apt / ...
• git
• heroku / clever / ...
• what else ?

(Of course this is hard because: 1: these systems are not always consistent internally 2: they are definitively not consistent among each others).