changelog: adds note about closing #9386

CHANGELOG.md

@@ -22,6 +22,7 @@
 * **SMTP**: Make it possible to set specific EHLO for smtp client. [#9319](https://github.com/grafana/grafana/issues/9319)
 * **Dataproxy**: Allow grafan to renegotiate tls connection [#9250](https://github.com/grafana/grafana/issues/9250)
 * **HTTP**: set net.Dialer.DualStack to true for all http clients [#9367](https://github.com/grafana/grafana/pull/9367)
+* **Alerting**: Add diff and percent diff as series reducers [#9386](https://github.com/grafana/grafana/pull/9386), thx [@shanhuhai5739](https://github.com/shanhuhai5739)
 
 ## Tech
 * **Go**: Grafana is now built using golang 1.9