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/button_led_2.py

@@ -0,0 +1,9 @@
+from gpiozero import LED, Button
+from signal import pause
+
+led = LED(17)
+button = Button(2)
+
+led.source = button.values
+
+pause()