Document env config

[tomschr]

Affected Documentation Section

Reference & User

Suggested Change

When the environment config is stable enough, we need to take care of documenting the following:

• the respective keys, their meaning, and the datatypes
  => This is pure referential matter and needs to go into a Reference
• using the config subcommand
  => This should cover how to view the env config with all resolved fields.

Additional Context

See related issue #21