Describe additional state for ToDo that might cause trouble

If we wait for lock transaction confirmations immediately after sending the transaction without saving this state to the DB this might cause locking the money twice.
An additional state is needed for such a scenario.

swap/src/protocol/alice/steps.rs

@@ -135,6 +135,9 @@ where
         .await?;
 
     // TODO(Franck): Wait for Monero to be confirmed once
+    //  Waiting for XMR confirmations should not be done in here, but in a separate
+    //  state! We have to record that Alice has already sent the transaction.
+    //  Otherwise Alice might publish the lock tx twice!
 
     event_loop_handle
         .send_message2(channel, alice::Message2 {