Use the state images in the readme file

Also checking in the generated png files to make
1. the images avaliable to be rendered on github page.
2. graphviz a soft dependency only necessary if you modify the dot files.

Author: hlovdal

examples/elevator/README.md

@@ -28,13 +28,14 @@ each other:
     - State: Moving
     - State: Panic
 
+![Elevator states](./elevator_state.png)
+
  2. Motor
     - State: Stopped
     - State: Up
     - State: Down
 
-
-[insert ascii-art here]
+![Machine states](./machine_state.png)
 
 A good state machine design avoids circular dependencies at all
 cost: While the elevator sends events to the motor, the motor NEVER