docs: update release notes

Author: ellemouton

docs/release-notes/release-notes-0.21.0.md

@@ -54,8 +54,14 @@
 
 ## Database
 
+* Freeze the [graph SQL migration 
+  code](https://github.com/lightningnetwork/lnd/pull/10338) to prevent the 
+  need for maintenance as the sqlc code evolves. 
+
 ## Code Health
 
 ## Tooling and Documentation
 
 # Contributors (Alphabetical Order)
+
+* Elle Mouton