docs: update release notes for 0.20

Author: yyforyongyu

docs/release-notes/release-notes-0.20.0.md

@@ -32,6 +32,12 @@
 ## Functional Updates
 
 ## RPC Updates
+* Previously the `RoutingPolicy` would return the inbound fee record in its
+  `CustomRecords` field, which is duplicated info as it's already presented in
+  fields `InboundFeeBaseMsat` and `InboundFeeRateMilliMsat`. This is now
+  [fixed](https://github.com/lightningnetwork/lnd/pull/9572), the affected RPCs
+  are `SubscribeChannelGraph`, `GetChanInfo`, `GetNodeInfo` and `DescribeGraph`.
+
 
 ## lncli Updates