f - Expand short_channel_id docs

Author: jkczyz

lightning/src/util/events.rs

@@ -204,6 +204,9 @@ pub enum Event {
 		/// The payment path that failed.
 		path: Vec<RouteHop>,
 		/// The channel responsible for the failed payment path.
+		///
+		/// If this is `Some`, then the corresponding channel should be avoided when the payment is
+		/// retried. May be `None` for older [`Event`] serializations.
 		short_channel_id: Option<u64>,
 #[cfg(test)]
 		error_code: Option<u16>,