Re-write ChannelManager summary documentation

Author: jkczyz

lightning/src/ln/channelmanager.rs

@@ -951,11 +951,28 @@ where
 	fn get_cm(&self) -> &ChannelManager<M, T, ES, NS, SP, F, R, L> { self }
 }
 
-/// Manager which keeps track of a number of channels and sends messages to the appropriate
-/// channel, also tracking HTLC preimages and forwarding onion packets appropriately.
+/// A lightning node's channel state machine and payment management logic.
 ///
-/// Implements [`ChannelMessageHandler`], handling the multi-channel parts and passing things through
-/// to individual Channels.
+/// [`ChannelManager`] is parameterized by a number of components, which in aggregate facilitate
+/// sending, forwarding, and receiving payments through lightning channels.
+/// - [`chain::Watch`] (typically [`ChainMonitor`]) for on-chain monitoring of transactions relevant
+///   to each channel
+/// - [`BroadcasterInterface`] for broadcasting transactions related to opening, funding, and
+///   closing channels
+/// - [`EntropySource`] for providing random data needed for cryptographic operations
+/// - [`NodeSigner`] for cryptographic operations scoped to the node
+/// - [`SignerProvider`] for providing signers whose operations are scoped to individual channels
+/// - [`FeeEstimator`] to determine transaction fee rates needed to have a transaction mined in a
+///   timely manner
+/// - [`Router`] for finding payment paths when initiating and retrying payments
+/// - [`Logger`] for logging operational information of varying degrees
+///
+/// It implements [`ChannelMessageHandler`] to handle off-chain channel activity from peers,
+/// [`MessageSendEventsProvider`] to similarly send such messages to peers, and [`EventsProvider`]
+/// to generate user-actionable [`Event`]s.
+///
+/// Additionally, [`ChannelManager`] implements both [`chain::Listen`] and [`chain::Confirm`] for
+/// notification of on-chain events.
 ///
 /// # Persistence
 ///
@@ -1005,6 +1022,7 @@ where
 /// [`SimpleArcChannelManager`] when you require a `ChannelManager` with a static lifetime, such as when
 /// you're using lightning-net-tokio.
 ///
+/// [`ChainMonitor`]: crate::chain::chainmonitor::ChainMonitor
 /// [`peer_disconnected`]: msgs::ChannelMessageHandler::peer_disconnected
 /// [`funding_created`]: msgs::FundingCreated
 /// [`funding_transaction_generated`]: Self::funding_transaction_generated