Convert recipe examples to includes

Makes it much easier to test things - no copying'n'pasting just run the
examples straight from the dir (after wiring stuff up)

docs/examples/robot_motion_1.py

@@ -0,0 +1,10 @@
+from gpiozero import Robot, MotionSensor
+from signal import pause
+
+robot = Robot(left=(4, 14), right=(17, 18))
+pir = MotionSensor(5)
+
+pir.when_motion = robot.forward
+pir.when_no_motion = robot.stop
+
+pause()