message: add note how to use UART_B
diff: @@ -11,3 +11,15 @@ To use UART connect it like this:
  The logic level of the ODrive is 3.3V. The GPIOs are 5V tolerant.
  You can use `odrv0.config.uart_a_baudrate` to change the baudrate and `odrv0.config.enable_uart_a` to disable/reenable UART_A. Currently the UART port runs both the [Native Protocol](native-protocol) and the [ASCII Protocol](ascii-protocol) at the same time.
  +
  +### How to use UART on GPIO3/4
  +
  +If you need GPIO1/2 for some function other than UART you can disable UART_A and instead use UART_B on GPIO3/4. Here's how you do it:
  +
  + odrv0.config.enable_uart_a = False
  + odrv0.config.gpio1_mode = GPIO_MODE_DIGITAL
  + odrv0.config.gpio2_mode = GPIO_MODE_DIGITAL
  + odrv0.config.enable_uart_b = True
  + odrv0.config.gpio3_mode = GPIO_MODE_UART_B
  + odrv0.config.gpio4_mode = GPIO_MODE_UART_B
  + odrv0.reboot()
  