Describe ConfirmationTarget::MaximumFeeEstimate more accurately

This isn't really just the maximum estimate that we want from our
fee estimator but rather the maximum estimate that we think is
reasonable to receive from our counterparty. Thus, we should really
describe it as such and suggest users add a fudge on top to
accomodate disagreements.

Author: TheBlueMatt

lightning/src/chain/chaininterface.rs

@@ -49,11 +49,14 @@ pub trait BroadcasterInterface {
 /// estimation.
 #[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
 pub enum ConfirmationTarget {
-	/// The most aggressive (i.e. highest) feerate estimate available.
+	/// The most aggressive feerate estimate which we think is reasonable.
 	///
 	/// This is used to sanity-check our counterparty's feerates and should be as conservative as
 	/// possible to ensure that we don't confuse a peer using a very conservative estimator for one
-	/// trying to burn channel balance to dust.
+	/// trying to burn channel balance to dust. To ensure that this is never lower than an honest
+	/// counterparty's feerate estimate you may wish to use a value which is higher than your
+	/// maximum feerate estimate, for example by adding a constant few-hundred or few-thousand
+	/// sats-per-kW.
 	MaximumFeeEstimate,
 	/// We have some funds available on chain which we need to spend prior to some expiry time at
 	/// which point our counterparty may be able to steal them.