Mention usage of pandas and seaborn (#1193)

Update the documentation to mention additional packages used in some python examples.

doc/tutorial/index.rst

@@ -4,7 +4,7 @@ Quick start
 ================================
 
 .. Note::
-    You can find some examples of full Arbor simulations in the ``python/examples`` directory of the `Arbor repository <https://github.com/arbor-sim/arbor>`_.
+    You can find some examples of full Arbor simulations in the ``python/examples`` directory of the `Arbor repository <https://github.com/arbor-sim/arbor>`_. Note that some examples use ``pandas`` and ``seaborn`` for analysis and plotting which are expected to be installed independently from Arbor.
 
 .. Todo::
     Add more in-depth tutorial-like pages building up examples here.