update README with docs update info

Author: drakejwong

README.md

@@ -59,3 +59,14 @@ poetry run pytest tests/test_dataset.py
 ```
 poetry run pytest -m "not integration"
 ```
+
+**Updating documentation:**
+We use [Sphinx](https://www.sphinx-doc.org/en/master/) to autogenerate our API Reference from docstrings.
+
+To test your local docstring changes, run the following commands from the repository's root directory:
+```
+poetry shell
+cd docs
+sphinx-autobuild . ./_build/html --watch ../nucleus
+```
+`sphinx-autobuild` will spin up a server on localhost (port 8000 by default) that will watch for and automatically rebuild a version of the API reference based on your local docstring changes.