docs: Mention JupyterLab and use heading

Mention JupyterLab in the FAQ. This is a useful addition
in case people are searching for it.

This commit also uses a second-level heading for questions in the FAQ
section. This will allow linking to specific questions.

doc/faq.rst

@@ -2,11 +2,13 @@
  Frequently Asked Questions
 ============================
 
-How can I use PyStan with Jupyter Notebook?
-  Use `nest-asyncio <https://pypi.org/project/nest-asyncio/>`_. This package is needed
-  because Jupter Notebook blocks the use of certain `asyncio
-  <https://docs.python.org/3/library/asyncio.html>`_ functions. (To verify this, try
-  running ``asyncio.run(asyncio.sleep(1))`` in a notebook.) If you would like to learn
-  more about the problem, see the following issue: `ipython/ipykernel#548
-  <https://github.com/ipython/ipykernel/issues/548>`_. This problem only affects Jupyter
-  Notebook. It does not affect IPython.
+How can I use PyStan with Jupyter Notebook or JupyterLab?
+---------------------------------------------------------
+
+Use `nest-asyncio <https://pypi.org/project/nest-asyncio/>`_. This package is needed
+because Jupter Notebook blocks the use of certain `asyncio
+<https://docs.python.org/3/library/asyncio.html>`_ functions. (To verify this, try
+running ``asyncio.run(asyncio.sleep(1))`` in a notebook.) If you would like to learn
+more about the problem, see the following issue: `ipython/ipykernel#548
+<https://github.com/ipython/ipykernel/issues/548>`_. This problem only affects Jupyter
+Notebook and derivatives. It does not affect IPython.