add controller and service class

src/main/java/com/example/calculatorwebservice/controller/CalculatorController.java

+package com.example.calculatorwebservice.controller;
+
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequestMapping("/calcualte")
+public class CalculatorController {
+}