Add comments to explain timeout functionality

The timeout functionality has changed, and it needs to be explained.
Timeouts because of lost sync bytes should be done on the 
opposite end if needed. Otherwise, the two sides get out of sync
every now and then.

Author: alrvid

libraries/Camera/examples/CameraCaptureRawBytes/CameraCaptureRawBytes.ino

@@ -64,10 +64,12 @@ void loop() {
     while(!Serial);
   }
 
-  // Time out after 2 seconds and send new data
+  // Time out after 2 seconds, which sets the (constant) frame rate
   bool timeoutDetected = millis() - lastUpdate > 2000;
 
   // Wait for sync byte and timeout
+  // Notice that this order must be kept, or the sync bytes will be
+  // consumed prematurely
   if ((!timeoutDetected) || (Serial.read() != 1))
   {
     return;