[nrf52,cdc] add doc

Author: tomaszduda23

content/components/uart.md

@@ -65,6 +65,9 @@ uart:
   Use of this setting enables half-duplex mode. Use the full pin schema and set `inverted: true` to invert logic levels.
 
 - **port** (*Optional*, string): Host platform only. Unix style name of the port to use.
+
+- **hardware_uart** (*Optional*, string): NRF52 platform only. Port to be used `USB_CDC` or `USB_CDC1`.
+
 - **rx_buffer_size** (*Optional*, int): The size of the buffer used for receiving UART messages. Increase if you use an
   integration that needs to read big payloads from UART. Defaults to `256`.