Add a small sentence that async-std does also include Mutex implementations

docs/src/overview.md

@@ -2,7 +2,7 @@
 
 `async-std` and `async-task` along with their [supporting libraries][organization] are a two libraries making your life in async programming easier. They provide fundamental implementations for downstream libraries and applications alike.
 
-`async-std` provides an interface to all important primitives: filesystem operations, network operations and concurrency basics like timers. It also exposes `async-task` in a model similar to the `thread` module found in the Rust standard lib. The name reflects the approach of this library: it is a closely modeled to the Rust main standard library as possible, replacing all components by async counterparts. You can read more about `async-std` in [the overview chapter][overview-std].
+`async-std` provides an interface to all important primitives: filesystem operations, network operations and concurrency basics like timers. It also exposes `async-task` in a model similar to the `thread` module found in the Rust standard lib. The name reflects the approach of this library: it is a closely modeled to the Rust main standard library as possible, replacing all components by async counterparts. This not only includes io primitives, but also `async/await` compatible versions of primitives like `Mutex`. You can read more about `async-std` in [the overview chapter][overview-std].
 
 `async-task` is a library for implementing asynchronous tasks quickly. For the purpose of this documentation, you will mainly interact with it through the `async_std::task` module. Still, it has some nice properties to be aware of, which you can read up on in the [`async-task` crate docs][task-docs].