Updated all serial in setup examples with a note about the serial check

libraries/Ethernet/examples/ChatServer/ChatServer.ino

@@ -41,7 +41,9 @@ void setup() {
   server.begin();
  // Open serial communications and wait for port to open:
   Serial.begin(9600);
-  while(!Serial) ;
+  // this check is only needed on the Leonardo:
+  while (!Serial) ;
+ ;
 
   Serial.print("Chat server address:");
   Serial.println(Ethernet.localIP());