Add sleep to infinite loop example in README (#755)

add sleep in `while True` loop to avoid using 100% CPU

See #754

Author: dlech

README.rst

@@ -50,6 +50,9 @@ to get started:
 .. code-block:: python
 
    #!/usr/bin/env python3
+   
+   from time import sleep
+   
    from ev3dev2.motor import LargeMotor, OUTPUT_A, OUTPUT_B, SpeedPercent, MoveTank
    from ev3dev2.sensor import INPUT_1
    from ev3dev2.sensor.lego import TouchSensor
@@ -107,6 +110,8 @@ before trying this out.
       else:
           leds.set_color("LEFT", "RED")
           leds.set_color("RIGHT", "RED")
+      # don't let this loop use 100% CPU
+      sleep(0.01)
 
 If you'd like to use a sensor on a specific port, specify the port like this: