Add explicit comparison to other (Cosmos / e2e) testing frameworks

[ivan-gavran]

We have a detailed README at the moment that contains all the necessary information.
However, it misses an emphasized comparison to other testing frameworks.
(Most of the first-time visitors to the repo will have the question in mind How does Atomkraft differ from my favourite/most familiar testing framework).

I suggest we add a subsection making an emphasis on automatic generation of large number of tests, with perhaps a side-by-side comparison with some other testing frameworks/methodologies.