Update CHANGES.md for release v2.1.0

Author: actions-user

CHANGES.md

@@ -8,13 +8,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### New
-- Add notification plugin support to mkp-builder (collects from `local/share/check_mk/notifications/`, creates `notifications.tar`)
-- Add notification plugin development guide (14-notifications.md) covering Discord/webhook examples, environment variables, testing
 
 ### Changed
 
 ### Fixed
 
+## 2.1.0 - 2025-11-19
+### New
+- Add notification plugin support to mkp-builder (collects from `local/share/check_mk/notifications/`, creates `notifications.tar`)
+- Add notification plugin development guide (14-notifications.md) covering Discord/webhook examples, environment variables, testing
+
 ## 2.0.3 - 2025-11-14
 ### New
 - refactored plugin guide with added snmp plugin info