Add additional docs for list_pending_payments

lightning/src/ln/channelmanager.rs

@@ -1642,6 +1642,11 @@ impl<M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelManager<M, T, K, F
 	}
 
 	/// Gets a list of payments in random order that are currently pending resolution.
+	///
+	/// This can be useful for figuring out whether or not a payment made needs to be retried.
+	/// In general, if it is not listed here, you should consider retrying it with a caveat: if a
+	/// payment is returned as [`RecentPaymentDetails::Fulfilled`], you may retry it, but should
+	/// not.
 	pub fn list_pending_payments(&self) -> Vec<RecentPaymentDetails> {
 		self.pending_outbound_payments.pending_outbound_payments.lock().unwrap().iter()
 			.filter_map(|(_, pending_outbound_payment)| match pending_outbound_payment {