esp32/boards/ARDUINO_NANO_ESP32: Clarify recovery instructions.

Signed-off-by: Sebastian Romero <s.romero@arduino.cc>

ports/esp32/boards/ARDUINO_NANO_ESP32/deploy.md

@@ -4,5 +4,10 @@ This board can programmed via DFU bootloader, using e.g. [dfu-util](http://dfu-u
 To enter the DFU bootloader, double tap the reset (blue) button, or you can use `machine.bootloader()` from the MicroPython REPL.
 
 ```bash
-dfu-util -d 0x2341:0x0070 -R -D build-ARDUINO_NANO_ESP32/micropython.bin
+dfu-util -d 0x2341:0x0070 -R -D build-ARDUINO_NANO_ESP32/micropython.app-bin
 ```
+
+Please note that the DFU bootloader comes factory flashed. Should you for any reason erase the
+entire flash, the DFU bootloader will have to be re-installed. Please follow the instructions
+[here](https://support.arduino.cc/hc/en-us/articles/9810414060188-Reset-the-Arduino-bootloader-on-the-Nano-ESP32)
+to do so.