Add note about field access after struct update syntax

src/ch05-01-defining-structs.md

@@ -154,7 +154,8 @@ Move”][move]<!-- ignore --> section. In this example, we can no longer use
 `active` and `sign_in_count` values from `user1`, then `user1` would still be
 valid after creating `user2`. Both `active` and `sign_in_count` are types that
 implement the `Copy` trait, so the behavior we discussed in the [“Stack-Only
-Data: Copy”][copy]<!-- ignore --> section would apply.
+Data: Copy”][copy]<!-- ignore --> section would apply. We can still use
+`user1.email` in this example, since its value was _not_ moved out.
 
 ### Using Tuple Structs Without Named Fields to Create Different Types