Document v2

[e-caste]

When v2 is ready, it needs to be properly documented for easy usage within our other projects (peracotta and turbofresa at the moment).

This is to answer specific questions one might have (for example: what's the difference between Product/Item and ProductToUpload/ItemToUpload?), the general usage/workflow needed to use this library in a project (e.g. first import this, then create a session like that, etc, best with some examples) and, last but not least, the specific usage of each API available in the PyTarallo.

[lvps]

The tests provide some examples for common (and less common) operations