Further document the initial routing table send.

As requested by Arik at lightningdevkit#435 (comment)

lightning/src/ln/msgs.rs

@@ -654,10 +654,11 @@ pub trait RoutingMessageHandler : Send + Sync {
 	fn handle_htlc_fail_channel_update(&self, update: &HTLCFailChannelUpdate);
 	/// Gets a subset of the channel announcements and updates required to dump our routing table
 	/// to a remote node, starting at the short_channel_id indicated by starting_point and
-	/// including batch_amount entries.
+	/// including the batch_amount entries immediately higher in numerical value than starting_point.
 	fn get_next_channel_announcements(&self, starting_point: u64, batch_amount: u8) -> Vec<(ChannelAnnouncement, ChannelUpdate, ChannelUpdate)>;
 	/// Gets a subset of the node announcements required to dump our routing table to a remote node,
-	/// starting at the node *after* the provided publickey and including batch_amount entries.
+	/// starting at the node *after* the provided publickey and including batch_amount entries
+	/// immediately higher (as defined by <PublicKey as Ord>::cmp) than starting_point.
 	/// If None is provided for starting_point, we start at the first node.
 	fn get_next_node_announcements(&self, starting_point: Option<&PublicKey>, batch_amount: u8) -> Vec<NodeAnnouncement>;
 	/// Returns whether a full sync should be requested from a peer.