#539 Checkstyle fixes

converter/src/main/java/com/iluwatar/converter/User.java

@@ -25,6 +25,9 @@ package com.iluwatar.converter;
 
 import java.util.Objects;
 
+/**
+ * User class
+ */
 public class User {
   private String firstName;
   private String lastName;

converter/src/main/java/com/iluwatar/converter/UserDto.java

@@ -26,6 +26,9 @@ package com.iluwatar.converter;
 
 import java.util.Objects;
 
+/**
+ * User DTO class
+ */
 public class UserDto {
 
   private String firstName;