Add a more complex example involving multi-part messages

Author: gummif

README.md

@@ -41,9 +41,8 @@ Supported platforms
 
 Examples
 ========
-This example requires at least C++11.
+These examples requires at least C++11.
 ```c++
-#include <string>
 #include <zmq.hpp>
 
 int main()
@@ -54,6 +53,36 @@ int main()
     sock.send(zmq::str_buffer("Hello, world"), zmq::send_flags::dontwait);
 }
 ```
+This a more complex example where we send and receive multi-part messages.
+```c++
+#include <iostream>
+#include <zmq_addon.hpp>
+
+int main()
+{
+    zmq::context_t ctx;
+    zmq::socket_t sock1(ctx, zmq::socket_type::pair);
+    zmq::socket_t sock2(ctx, zmq::socket_type::pair);
+    sock1.bind("inproc://test");
+    sock2.connect("inproc://test");
+
+    std::array<zmq::const_buffer, 2> send_msgs = {
+        zmq::str_buffer("foo"),
+        zmq::str_buffer("bar!")
+    };
+    if (!zmq::send_multipart(sock1, send_msgs))
+        return 1;
+
+    std::vector<zmq::message_t> recv_msgs;
+    const auto ret = zmq::recv_multipart(
+        sock2, std::back_inserter(recv_msgs));
+    if (!ret)
+        return 1;
+    std::cout << "Got " << *ret
+              << " messages" << std::endl;
+    return 0;
+}
+```
 
 Contribution policy
 ===================