message: add instructions on disabling PWM input
diff: @@ -108,6 +108,7 @@ As an example, we'll configure GPIO4 to control the angle of axis 0. We want the
  In [3]: odrv0.config.gpio4_pwm_mapping.endpoint = odrv0.axis0.controller._remote_attributes['pos_setpoint']
  ```
  + Note: you can disable the input by setting `odrv0.config.gpio4_pwm_mapping.endpoint = None`
  4. Save the configuration and reboot
  ```
  In [4]: odrv0.save_configuration()
  