example to call tud_init() after freeRTOS kernel is started

add note for usb init when using with RTOS

examples/device/cdc_msc_freertos/src/main.c

@@ -83,7 +83,6 @@ void cdc_task(void* params);
 int main(void)
 {
   board_init();
-  tusb_init();
 
   // soft timer for blinky
   blinky_tm = xTimerCreateStatic(NULL, pdMS_TO_TICKS(BLINK_NOT_MOUNTED), true, NULL, led_blinky_cb, &blinky_tmdef);
@@ -116,6 +115,10 @@ void usb_device_task(void* param)
 {
   (void) param;
 
+  // This should be called after scheduler/kernel is started.
+  // Otherwise it could cause kernel issue since USB IRQ handler does use RTOS queue API.
+  tusb_init();
+
   // RTOS forever loop
   while (1)
   {