Sphinx doc gen excludes `__init__` docstrings

[EricSchrock]

I noticed that the current Sphinx documentation generation does not include docstrings from __init__ methods, which means some important documentation is being excluded from the readthedocs page.

Example: https://pyhealth.readthedocs.io/en/latest/api/datasets/pyhealth.datasets.ChestXray14Dataset.html

ChatGPT claims the solution is as simple as adding autoclass_content = "both" to conf.py.

Alternatively, it claims this should work.

.. autoclass:: pyhealth.datasets.ChestXray14Dataset
   :members:
   :special-members: __init__
   :undoc-members:
   :show-inheritance:

Or we could standardize on just using either the class docstring or the init doc string...