fix missing variable and add explanations

docs/python/simctrl/savstate.rst

@@ -54,6 +54,8 @@ SaveState
 
             h.continuerun(5 * ms)
 
+            # this function is here solely for the demo to show the staet has changed
+            # there's no need to do this in your code
             def get_state():
                 return (
                     soma(0.5).v,
@@ -71,6 +73,10 @@ SaveState
 
             h.continuerun(10 * ms)
 
+            # store the current state (don't need to do this in general, this is just to show
+            # that we're no longer here after the restore)
+            s2 = get_state()
+
             # go back to the way things were at 5 * ms (when we called s.save())
             s.restore()