message: comment about caveat of current transfer rate refresh
diff: @@ -712,6 +712,16 @@ pub fn with_fetch_options(
  )
  } else {
  // Receiving objects.
  + //
  + // # Caveat
  + //
  + // Progress bar relies on git2 calling `transfer_progress`
  + // to update its transfer rate, but we cannot guarantee a
  + // periodic call of that callback. Thus if we don't receive
  + // any data for, say, 10 seconds, the rate will get stuck
  + // and never go down to 0B/s.
  + // In the future, we need to find away to update the rate
  + // even when the callback is not called.
  let now = Instant::now();
  // Scrape a `received_bytes` to the counter every 300ms.
  if now - last_update > Duration::from_millis(300) {
  