Add example usage of library to the repo

[eirenik0]

Currently officially available only old docs for 3.x which lead to bad user expirience (see #47). Before official doc would be updated need to add basic doc about usage.

The following items should be added:

1. Installing and initialization of different eyes libs
2. Basic overview of Configuration class and describe attributes
3. Overview of possibilities of Fluent interface (check() and Target)
4. Using of close()
5. As a bonus, write some tips to use with pytest