Mention required dependencies in docs (#77)

Fixes https://github.com/tokio-rs/axum/issues/70

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Improve documentation for routing ([#71](https://github.com/tokio-rs/axum/pull/71))
 - Clarify required response body type when routing to `tower::Service`s ([#69](https://github.com/tokio-rs/axum/pull/69))
 - Add `axum::body::box_body` to converting an `http_body::Body` to `axum::body::BoxBody` ([#69](https://github.com/tokio-rs/axum/pull/69))
+- Mention required dependencies in docs ([#77](https://github.com/tokio-rs/axum/pull/77))
 - Fix WebSockets failing on Firefox ([#76](https://github.com/tokio-rs/axum/pull/76))
 
 ## Breaking changes

src/lib.rs

@@ -17,6 +17,7 @@
 //! - [Sharing state with handlers](#sharing-state-with-handlers)
 //! - [Routing to any `Service`](#routing-to-any-service)
 //! - [Nesting applications](#nesting-applications)
+//! - [Required dependencies](#required-dependencies)
 //! - [Examples](#examples)
 //! - [Feature flags](#feature-flags)
 //!
@@ -624,6 +625,27 @@
 //! # };
 //! ```
 //!
+//! # Required dependencies
+//!
+//! To use Axum there are a few dependencies you have pull in as well:
+//!
+//! ```toml
+//! [dependencies]
+//! axum = "<latest-version>"
+//!
+//! # For http types like `StatusCode`, `Method`, and `Response`
+//! http = "<latest-version>"
+//!
+//! # "full" isn't strictly necessary for tokio and hyper but its the
+//! # easiest way to get started.
+//! hyper = { version = "<latest-version>", features = ["full"] }
+//! tokio = { version = "<latest-version>", features = ["full"] }
+//!
+//! # Not strictly necessary but helpful for testing. There is a
+//! # testing example in the repo that shows how to test axum apps.
+//! tower = "<latest-version>"
+//! ```
+//!
 //! # Examples
 //!
 //! The axum repo contains [a number of examples][examples] that show how to put all the