Add example of using with Arduino Ethernet Shield (#111)

examples/ArduinoEthernetShield/ArduinoEthernetShield.ino

@@ -0,0 +1,45 @@
+#include <EthernetUdp.h>
+#include <NTPClient.h>
+
+#define ethernetShieldPin 10  // Most Arduino shields
+// #define ethernetShieldPin 5   // MKR ETH shield
+// #define ethernetShieldPin 0   // Teensy 2.0
+// #define ethernetShieldPin 20  // Teensy++ 2.0
+// #define ethernetShieldPin 15  // ESP8266 with Adafruit Featherwing Ethernet
+// #define ethernetShieldPin 33  // ESP32 with Adafruit Featherwing Ethernet
+
+byte localMac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
+unsigned int localUdpPort = 8888;
+EthernetUDP udp;
+
+NTPClient timeClient(udp);
+
+void setup() {
+  Serial.begin(115200);
+  while (!Serial) {
+    ; // wait for serial port to connect. Needed for native USB port only
+  }
+  
+  Ethernet.init(ethernetShieldPin);
+  Serial.println("Initialize Ethernet with DHCP");
+  if (Ethernet.begin(localMac) == 0) {
+    Serial.println("Failed to configure Ethernet using DHCP");
+    if (Ethernet.hardwareStatus() == EthernetNoHardware) {
+      Serial.println("Ethernet shield was not found.");
+    }
+    if (Ethernet.linkStatus() == LinkOFF) {
+      Serial.println("Ethernet cable is not connected.");
+    }
+    while (true) {
+      delay(1);
+    }
+  }
+  udp.begin(localUdpPort);
+}
+
+void loop() {
+  if(timeClient.update()) {
+    Serial.print("Updated current time: ");
+    Serial.println(timeClient.getFormattedTime());
+  }
+}