f add note about calling update_channel

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -1895,6 +1895,8 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 	/// to inform the network about the uselessness of these channels.
 	///
 	/// This method handles all the details, and must be called roughly once per minute.
+	///
+	/// Note that in some rare cases this may generate a `chain::Watch::update_channel` call.
 	pub fn timer_chan_freshness_every_min(&self) {
 		let _persistence_guard = PersistenceNotifierGuard::new(&self.total_consistency_lock, &self.persistence_notifier);
 		self.process_background_events();