Clarify that user1 can't be used as a whole instance. Fixes #2978.

Author: carols10cents

src/ch05-01-defining-structs.md

@@ -148,13 +148,13 @@ the struct’s definition.
 Note that the struct update syntax uses `=` like an assignment; this is because
 it moves the data, just as we saw in the [“Variables and Data Interacting with
 Move”][move]<!-- ignore --> section. In this example, we can no longer use
-`user1` after creating `user2` because the `String` in the `username` field of
-`user1` was moved into `user2`. If we had given `user2` new `String` values for
-both `email` and `username`, and thus only used the `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.
+`user1` as a whole after creating `user2` because the `String` in the
+`username` field of `user1` was moved into `user2`. If we had given `user2` new
+`String` values for both `email` and `username`, and thus only used the
+`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.
 
 ### Using Tuple Structs Without Named Fields to Create Different Types