message: Add ordering note
diff: //! tokio::run(fut);
  //! ```
  //!
  +//! # Behavior
  +//!
  +//! Calling a method like `Client::query` on its own does nothing. The associated request is not sent to the database
  +//! until the future returned by the method is first polled. Requests are executed in the order that they are first
  +//! polled, not in the order that their futures are created.
  +//!
  //! # Pipelining
  //!
  //! The client supports *pipelined* requests. Pipelining can improve performance in use cases in which multiple,
  