Merge pull request #296 from deepikabhavnani/udp_socket

UDP sockect doc update

Author: Amanda Butler

docs/reference/api/connectivity/networksocket/UDPSocket.md

@@ -2,6 +2,14 @@
 
 The UDPSocket class provides the ability to send packets of data over UDP, using the `sendto` and `recvfrom` member functions. Packets can be lost or arrive out of order, so we suggest using a [TCPSocket](/docs/v5.6/reference/tcpsocket.html) when you require guaranteed delivery.
 
+The constructor takes in the NetworkStack pointer to open the socket on the specified NetworkInterface. If you do not pass in the constructor, then you must call `open` to initialize the socket.
+
 ### UDPSocket class reference
 
 [![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/v5.6/mbed-os-api-doxy/class_u_d_p_socket.html)
+
+### UDPSocket Example
+
+Here is a UDP example to read the current UTC time by sending a request to the NIST Internet Time Service. 
+
+[![View code](https://www.mbed.com/embed/?url=https://os.mbed.com/teams/mbed_example/code/mbed-os-example-udp-sockets)](https://os.mbed.com/teams/mbed_example/code/mbed-os-example-udp-sockets/file/cf516d904427/main.cpp)