UART added

Core/Inc/stm32f1xx_it.h

@@ -57,6 +57,7 @@ void PendSV_Handler(void);
 void SysTick_Handler(void);
 void DMA1_Channel5_IRQHandler(void);
 void TIM2_IRQHandler(void);
+void USART2_IRQHandler(void);
 /* USER CODE BEGIN EFP */
 
 /* USER CODE END EFP */