Add missing wumbo feature bit docs

Author: valentinewallace

lightning/src/ln/features.rs

@@ -39,6 +39,8 @@
 //!     (see [BOLT-4](https://github.com/lightning/bolts/blob/master/04-onion-routing.md) for more information).
 //! - `BasicMPP` - requires/supports that a node can receive basic multi-part payments
 //!     (see [BOLT-4](https://github.com/lightning/bolts/blob/master/04-onion-routing.md#basic-multi-part-payments) for more information).
+//! - `Wumbo` - requires/supports that a node create large channels. Called `option_support_large_channel` in the spec.
+//!     (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md#the-open_channel-message) for more information).
 //! - `ShutdownAnySegwit` - requires/supports that future segwit versions are allowed in `shutdown`
 //!     (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md) for more information).
 //! - `ChannelType` - node supports the channel_type field in open/accept