Add short manual with examples

[ondrej33]

As the amount of functionality grows and the project slowly becomes more complex (and sometimes complicated to follow), we should add a short tutorial/manual. We should describe the input and output formats and explain subtle differences between the various supported versions of model-checking procedures. The manual/tutorial should come with clear examples for each supported task. This could be done as a Rust documentation-only module.

This will come in handy even more once the tool itself is extended by the latest functionality of the library (#15).