docs: update release notes

Signed-off-by: Mohammad Tayyab <Mohammad.Tayyab@neustrom.de>

Author: Mohammad-Tayyab-Frequenz

RELEASE_NOTES.md

@@ -5,7 +5,7 @@
 <!-- Here goes a general summary of what this release is about -->
 
 ## Upgrading
-
+* Microgrid_config is updated from AC_ACTIVE_POWER to AC_POWER_ACTIVE in accordance with the update in client-reporting - v0.20.0
 <!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
 
 ## New Features