The `dfu-util` command uses `--device $(DFU_USB_ID)`, where `DFU_USB_ID` is derived from `USB_VID` and `USB_PID` to specify the DFU device to use. Without specifying `USB_VID` and `USB_PID` in the make command, `dfu-util` is called with `--device :`, which only works if there is only one DFU device. Also, the STM32 make system forbids the use of `dfu-util` as programmer without setting the variable `DFU_USB_ID`. Therefore, the documentation is changed to use `USB_VID`/`USB_PID` or `DFU_USB_ID` in the make command.