mention atomic primitive types after mutex & rwlock

posts/tour-of-rusts-standard-library-traits.md

@@ -1150,7 +1150,7 @@ unsafe auto trait Sync {}
 
 If a type is `Send` that means it's safe to send between threads. If a type is `Sync` that means it's safe to share references of it between threads. In more precise terms some type `T` is `Sync` if and only if `&T` is `Send`.
 
-Almost all types are `Send` and `Sync`. The only notable `Send` exception is `Rc` and the only notable `Sync` exceptions are `Rc`, `Cell`, `RefCell`. If you need a `Send` version of `Rc` use `Arc`. If you need a `Sync` version of `Cell` or `RefCell` use `Mutex` or `RwLock`.
+Almost all types are `Send` and `Sync`. The only notable `Send` exception is `Rc` and the only notable `Sync` exceptions are `Rc`, `Cell`, `RefCell`. If we need a `Send` version of `Rc` we can use `Arc`. If we need a `Sync` version of `Cell` or `RefCell` we can `Mutex` or `RwLock`. Although if we're using the `Mutex` or `RwLock` to just wrap a primitive type it's often better to use the atomic primitive types provided by the standard library such as `AtomicBool`, `AtomicI32`, `AtomicUsize`, and so on.
 
 That almost all types are `Sync` might be a surprise to some people, but yup, it's true even for types without any internal synchronization. This is possible thanks to Rust's strict borrowing rules.