Update FirebaseSerialClient.ino

Author: ed7coyne

examples/FirebaseSerialClient/FirebaseSerialClient.ino

@@ -32,7 +32,7 @@ const String auth = "";
 bool initialized = false;
 
 void setup() {
-  // Connect to pc over usb.
+  // Connect to pc over usb for debug output.
   Serial.begin(9600);
 
   // Connect to chiplet over the Serial1 port (pins 19 and 18).