Merge pull request #2361 from RalfJung/atomic

link to stdlib atomic docs

Author: carols10cents

src/ch16-03-shared-state.md

@@ -176,10 +176,12 @@ Fortunately, `Arc<T>` *is* a type like `Rc<T>` that is safe to use in
 concurrent situations. The *a* stands for *atomic*, meaning it’s an *atomically
 reference counted* type. Atomics are an additional kind of concurrency
 primitive that we won’t cover in detail here: see the standard library
-documentation for `std::sync::atomic` for more details. At this point, you just
+documentation for [`std::sync::atomic`] for more details. At this point, you just
 need to know that atomics work like primitive types but are safe to share
 across threads.
 
+[`std::sync::atomic`]: ../std/sync/atomic/index.html
+
 You might then wonder why all primitive types aren’t atomic and why standard
 library types aren’t implemented to use `Arc<T>` by default. The reason is that
 thread safety comes with a performance penalty that you only want to pay when