Minor documentation clarifications in Pipette.starting_tip.

Not sure if these are worthwhile.

api/src/opentrons/protocol_api/instrument_context.py

@@ -120,6 +120,10 @@ def starting_tip(self) -> Union[labware.Well, None]:
 
         See :py:meth:`.pick_up_tip()`.
 
+        The well must be from one of the tip racks in :py:obj:`.tip_racks`.
+        See :ref:`new-well-access`.
+        The default is ``None``, meaning the pipette will start at the first tip.
+
         .. note::
 
             In robot software versions 6.3.0 and 6.3.1, protocols specifying API level