WiFiTime: add print about minimum required firmware version

Author: pennam

libraries/WiFiS3/examples/WiFiTime/WiFiTime.ino

@@ -80,6 +80,7 @@ void loop() {
   }
   else {
     Serial.println("Error during reading epoch time.");
+    Serial.println("Make sure your WiFi firmware version is greater than 0.4.2");
   }
 
   Serial.println();