Update README.md

Fixed an error in a comment.
Was throwing `no matching function for call to 'NTPClient::NTPClient(const char [20], int, int)' ` otherwise

Author: g-goessel

README.md

@@ -22,7 +22,7 @@ NTPClient timeClient(ntpUDP);
 
 // You can specify the time server pool and the offset, (in seconds)
 // additionaly you can specify the update interval (in milliseconds).
-// NTPClient timeClient("europe.pool.ntp.org", 3600, 60000);
+// NTPClient timeClient(ntpUDP, "europe.pool.ntp.org", 3600, 60000);
 
 void setup(){
   Serial.begin(11520);