clientv3/doc: Improve error handling comment
// } else if err == context.DeadlineExceeded {
// // ctx is attached with a deadline and it exceeded
// } else if err == rpctypes.ErrEmptyKey {
-// // client-side error: key argument is empty
+// // client-side error: key is not provided
// } else if ev, ok := status.FromError(err); ok {
// code := ev.Code()
// if code == codes.DeadlineExceeded {
