Add version note in Confirm docs

While now `ChannelManager` will only return previously confirmed
transactions, we can't ensure the same for `ChainMonitor`, as we need to
maintain backwards compatibility with version prior to 0.0.113, at which
we started tracking the block hash in `ChannelMonitor`s. We therefore
add a note to the docs stating that users need to track confirmations on
their own for channels created prior to 0.0.113.

Author: tnull

lightning/src/chain/mod.rs

@@ -176,6 +176,9 @@ pub trait Confirm {
 	/// Returns transactions that must be monitored for reorganization out of the chain along
 	/// with the hash of the block as part of which it had been previously confirmed.
 	///
+	/// Note that the returned `Option<BlockHash>` might be `None` for channels created with LDK
+	/// 0.0.112 and prior, in which case you need to manually track previous confirmations.
+	///
 	/// Will include any transactions passed to [`transactions_confirmed`] that have insufficient
 	/// confirmations to be safe from a chain reorganization. Will not include any transactions
 	/// passed to [`transaction_unconfirmed`], unless later reconfirmed.