message: docs(body): add links to to_bytes and aggregate
  Since these two functions are not methods on the `Body`, they aren't
  very discoverable. So a note in the docs would definitely be helpful.
diff: @@ -29,6 +29,9 @@ type TrailersSender = oneshot::Sender<HeaderMap>;
  ///
  /// A good default [`HttpBody`](crate::body::HttpBody) to use in many
  /// applications.
  +///
  +/// Note: To read the full body, use [`body::to_bytes`](crate::body::to_bytes)
  +/// or [`body::aggregate`](crate::body::aggregate).
  #[must_use = "streams do nothing unless polled"]
  pub struct Body {
  kind: Kind,
  