Improve getting started instructions

[copernico]

The instructions at https://github.com/SAP/credential-digger#install should include some details as to what values should be put in the two fields:

test_model=
path_model=

Actually, a comment in the sample .env file would do.

[marcorosa]

I agree.
I added a sample link and update the README with the instructions on how to use the models in the container.

[copernico]

Hi @marcorosa, I would advise to put all that is needed right in the section https://github.com/SAP/credential-digger#install

I would expect that when I run the steps in that section I end up with a fully functional instance (which is not the case, because I get no rules).

Overall, I would suggest to provide a very simple path from zero to a fully working instance of the tool in one clear set of steps. Optional or alternative ways should be identified as such and documented separately. Right now the readme provides too much information and alternatives, but not the single one-stop-shop for the curious newcomer and prospective adopter.

EDIT: also the section https://github.com/SAP/credential-digger#architecture should be moved down in the readm, or to a separate file altogether (better): that breaks the flow from the high-level description of what the tool does to how to actually try it; the question about how it is architected come later and only for a limited class of users.