Comment improvement for S0 USBD example

readme.mk file in master/series0/usbd/usbd_cdc_uart_bridge
```
Note: the Drivers/cdc.c file uses the DMA and therefore is not compatible with
the GG11's LDMA. Therefore, this repo has a src/cdc_gg11.c file that is simply a
port of the Drivers/cdc.c file to use the LDMA instead.
```
looks the file was not cdc_gg11.c