Add module docstrings

[RobertCraigie]

Problem

We could improve the readability / experience reading through the library source code if there were module level docstrings.

Suggested solution

All python modules should include a docstring explaining what the purpose of the module is:

"""
prisma.client
~~~~~~~~~~~~~

Main interface for the Client API - handles connecting, disconnecting
and querying the underlying Prisma Engine.

:auto-generated:
"""

For contributors

This is a fairly simple change but it may not be exactly clear what each module does - if you need any help feel free to ask a question on the discord.

If you update auto-generated modules make sure you update the snapshots!

[Snipy7374]

Hi, i would like to work on this

[RobertCraigie]

Amazing! Let me know if you have any questions!