docs: add release notes

docs/release-notes/release-notes-0.14.0.md

@@ -38,6 +38,18 @@ instantaneous. Read the [guide on leader
 election](https://github.com/lightningnetwork/lnd/blob/master/docs/leader_election.md)
 for more information.
 
+### In-memory path finding
+
+Finding a path through the channel graph for sending a payment doesn't involve
+any database queries anymore. The [channel graph is now kept fully
+in-memory](https://github.com/lightningnetwork/lnd/pull/5642) for up a massive
+performance boost when calling `QueryRoutes` or any of the `SendPayment`
+variants. Keeping the full graph in memory naturally comes with increased RAM
+usage. Users running `lnd` on low-memory systems are advised to run with the
+`routing.strictgraphpruning=true` configuration option that more aggressively
+removes zombie channels from the graph, reducing the number of channels that
+need to be kept in memory.
+
 ## Protocol Extensions
 
 ### Explicit Channel Negotiation