Add example of struct update syntax

struct_example/src/main.rs

@@ -7,15 +7,23 @@ struct User {
 }
 
 fn build_user(email: String, username: String) -> User {
-     User {
+    User {
-         email,
+        email,
-	 username,
+        username,
-	 active: true,
+        active: true,
-	 sign_in_count: 0,
+        sign_in_count: 0,
-     }
+    }
 }
 
 fn main() {
     let user = build_user(String::from("Heisenberg"), String::from("mail@mail.com"));
     println!("Hello to the User: {:?}!", user);
+
+    let user2 = User {
+        username: String::from("Jesse"),
+        email: String::from("mail@mail.com"),
+        ..user
+    };
+
+    println!("Hello to the User: {:?}!", user2);
 }