[Documentation] Relationship between digga API and raw flake API/output

[DrPyser]

To properly understand how to use Digga in the context of the general nix/os ecosystem and properly integrate with other non-digga tooling, it would be very helpful to provide in the documentation a description of how the Digga API(lib.mkFlake) relates to the standard flake output interface.
One who has just started to understand Nix Flakes should be able to build on that knowledge to understand and use digga, and not simply have to relearn another opaque API.

For example,

• how does the nixos attribute relates to the nixosConfigurations flake output attribute
• homeConfigurations, homeConfigurationsPortable relates to what home-manager might expect
• packages, containers, ...

Thanks for this work!