add comment in peripheral pin of DISCO_L476VG so that

the user is aware of conflicts

Author: adustm

targets/TARGET_STM/TARGET_STM32L4/TARGET_STM32L476xG/TARGET_DISCO_L476VG/PeripheralPins.c

@@ -275,8 +275,8 @@ const PinMap PinMap_SPI_SSEL[] = {
 };
 
 const PinMap PinMap_CAN_RD[] = {
-    {PB_8 , CAN_1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_NOPULL, GPIO_AF9_CAN1)},
-    {PA_11, CAN_1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_NOPULL, GPIO_AF9_CAN1)},
+    {PB_8 , CAN_1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_NOPULL, GPIO_AF9_CAN1)}, // warning: pin used by gyroscope
+    {PA_11, CAN_1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_NOPULL, GPIO_AF9_CAN1)}, // warning: pin used by USB
     {NC,    NC,    0}
 };