f Add lightning-liquidtity as reference implementation

Author: tnull

blip-0050.md

@@ -17,6 +17,13 @@ peer-to-peer messages to allow clients to request services from the LSP.
 
 This bLIP is licensed under the MIT license.
 
+## Reference Implementation
+
+A reference implementation of this protocol can be found as part of the
+[`lightning-liquidity`][] crate.
+
+[`lightning-liquidity`]: https://github.com/lightningdevkit/rust-lightning/tree/main/lightning-liquidity
+
 ### Actors
 
 The 'LSP' is the API provider, and acts as the server.