fix: apply feedback from janny

docs/site/Validation-controller-layer.md

@@ -19,6 +19,8 @@ area code of a phone number usually depends on the geolocation.
 The simplest way is to apply the validation function in the controller method.
 For example:
 
+{% include code-caption.html content="/src/controllers/coffee-shop.controller.ts" %}
+
 ```ts
 // create a validatePhoneNum function and call it here
 if (!this.validatePhoneNum(coffeeShop.phoneNum, coffeeShop.city))