f fix docs

Author: TheBlueMatt

lightning/src/ln/channel.rs

@@ -3561,7 +3561,9 @@ impl<Signer: Sign> Channel<Signer> {
 	/// further details on the optionness of the return value.
 	/// If our balance is too low to cover the cost of the next commitment transaction at the
 	/// new feerate, the update is cancelled.
-	/// You MUST call send_commitment prior to any other calls on this Channel
+	///
+	/// You MUST call send_commitment prior to any other calls on this Channel if
+	/// `force_holding_cell` is false.
 	fn send_update_fee<L: Deref>(&mut self, feerate_per_kw: u32, mut force_holding_cell: bool, logger: &L) -> Option<msgs::UpdateFee> where L::Target: Logger {
 		if !self.is_outbound() {
 			panic!("Cannot send fee from inbound channel");