docs: add release notes

Author: Euler-B

docs/release-notes/release-notes-0.20.1.md

@@ -103,6 +103,13 @@
    for conservative budgeting and includes griefing protection by limiting the
    number of probed LSPs. It enhances the previous LSP design by being more
    generic and more flexible.
+ 
+ * The `listchannels` RPC now [exposes the actual 
+   spendable balance](https://github.com/lightningnetwork/lnd/pull/10624)
+   by adding `local_spendable_balance` and `remote_spendable_balance` fields. 
+   This provides users with a precise view of their actionable liquidity by 
+   correctly accounting for channel reserves and funds currently tied up in 
+   in-flight HTLCs.
 
 ## lncli Updates