We cannot use `puddl config update` to initialize the config, because
`puddl.cli.root()` always reads it and fails with KeyError.
We want to keep both the simplicity of hooking config reading into
`root()` and the explictness of failing if there is something missing
[1].
For now: use plain python with click (that we depend on anyways) to
initialize the config.

[1] Errors should never pass silently.
    Unless explicitly silenced.