Update "Instancing" with PhysicsMaterial

(cherry picked from commit d9cdcdad320a1088acb8a353b339cfe2b7ff88fc)

getting_started/step_by_step/instancing.rst

@@ -90,8 +90,17 @@ Run the scene again and all of the balls will fall.
 Editing instances
 -----------------
 
-Open the ``Ball`` scene and change the ``Bounce`` property in the Inspector
-to `1`. Press "Play" and notice that all of the instanced balls are now
+Open the ``Ball`` scene and add a ``PhysicsMaterial`` by clicking on the down
+arrow and selecting "New PhysicsMaterial".
+
+.. image:: img/instancing_physicsmat1.png
+
+Then, expand the material by clicking on it, and set the ``Bounce`` property
+to ``1``.
+
+.. image:: img/instancing_physicsmat2.png
+
+Press "Play" and notice that all of the instanced balls are now
 much more bouncy. Because the instanced balls are based on the saved scene,
 changes to that scene will affect all instances.