Add an example to the readme for futures (#4)

And add the example under examples/ so we know when it breaks.

examples/readme_future.rs

@@ -0,0 +1,36 @@
+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// Licensed under the MIT License, <LICENSE or http://opensource.org/licenses/MIT>.
+// This file may not be copied, modified, or distributed except according to those terms.
+
+#![feature(conservative_impl_trait, plugin)]
+#![plugin(tarpc_plugins)]
+
+extern crate futures;
+#[macro_use]
+extern crate tarpc;
+
+use tarpc::util::{FirstSocketAddr, Never};
+use tarpc::sync::Connect;
+
+service! {
+    rpc hello(name: String) -> String;
+}
+
+#[derive(Clone)]
+struct HelloServer;
+
+impl FutureService for HelloServer {
+    type HelloFut = futures::Finished<String, Never>;
+
+    fn hello(&self, name: String) -> Self::HelloFut {
+        futures::finished(format!("Hello, {}!", name))
+    }
+}
+
+fn main() {
+    let addr = "localhost:10000";
+    let _server = HelloServer.listen(addr.first_socket_addr());
+    let client = SyncClient::connect(addr).unwrap();
+    println!("{}", client.hello("Mom".to_string()).unwrap());
+}