text: Title: Add module docstrings
  Body: ## Problem
  
  <!-- A clear and concise description of what the problem is. Ex. I'm always frustrated when [...] -->
  
  We could improve the readability / experience reading through the library source code if there were module level docstrings.
  
  ## Suggested solution
  
  <!-- A clear and concise description of what you want to happen. -->
  
  All python modules should include a docstring explaining what the purpose of the module is:
  
  ```py
  """
  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](https://discord.gg/HpFaJbepBH).
  
  If you update auto-generated modules make sure you [update the snapshots](https://prisma-client-py.readthedocs.io/en/stable/contributing/contributing/#snapshot-tests)!