Add docs on duration -- revealer should use duration shorter than cou…

…nterparty

frame/atomic-swap/src/lib.rs

@@ -138,7 +138,9 @@ decl_module! {
  /// - `target`: Receiver of the atomic swap.
  /// - `hashed_proof`: The blake2_256 hash of the secret proof.
  /// - `balance`: Funds to be sent from origin.
- /// - `duration`: Locked duration of the atomic swap.
+ /// - `duration`: Locked duration of the atomic swap. For safety reasons, it is recommended
+ /// that the revealer uses a shorter duration than the counterparty, to prevent the
+ /// situation where the revealer reveals the proof too late around the end block.
  #[weight = T::DbWeight::get().reads_writes(1, 1).saturating_add(40_000_000)]
  fn create_swap(
  origin,