message: update and comment the assert on the selection policy
  we need to remember to update the algorithm when we extend the options
  for selection policy
diff: @@ -95,7 +95,12 @@ impl SelectionAlgorithm for LinearFee {
  , O : 'b + Iterator<Item = &'b TxOut> + Clone
  , Addressing: 'a
  {
  - debug_assert!(policy == SelectionPolicy::FirstMatchFirst);
  + // kind reminder to update the algorithm once we start to implement
  + // better kind of selection policy
  + debug_assert!(
  + policy == SelectionPolicy::FirstMatchFirst,
  + "Only supported selection policy here is FirstMatchFirst"
  + );
  // note: we cannot use `is_empty()` because it is an `ExactSizeIterator`
  // and it does not expose this function directly.
  