Update README.md

mapstruct/src/main/java/com/baeldung/mapper/CarMapper.java

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+package com.baeldung.mapper;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.factory.Mappers;
+
+import com.baeldung.dto.CarDTO;
+import com.baeldung.entity.Car;
+
+@Mapper
+public interface CarMapper {
+    
+    CarMapper INSTANCE = Mappers.getMapper(CarMapper.class);
+    
+    CarDTO carToCarDTO(Car car);
+}