text: Title: Add FAQ section on parametrizing notebooks
  Body: Notebook tasks require a `parameters` cell. If they don't have one, we raise the following error:
  
  ```pytb
    File "/Users/Edu/miniconda3/envs/ml-testing/lib/python3.9/site-packages/ploomber/sources/notebooksource.py", line 244, in _post_init_validation
      raise SourceInitializationError(msg)
  ploomber.exceptions.SourceInitializationError: Notebook "/Users/Edu/dev/ml-testing/analysis.ipynb" does not have a cell tagged "parameters". Add a cell at the top and tag it as "parameters". Click here for instructions: https://papermill.readthedocs.io/en/stable/usage-parameterize.html
  ```
  
  As you can see, we link to: https://papermill.readthedocs.io/en/stable/usage-parameterize.html
  
  However, papermill's docs only cover ipynb files, not py so we need to write our own help page
  
  Add file here: https://github.com/ploomber/ploomber/tree/master/doc/user-guide/faq