docs: add note about closing #6740

CHANGELOG.md

@@ -7,6 +7,7 @@
 ### Enhancements
 * **Postgres**: Add support for Certs for Postgres database [#6655](https://github.com/grafana/grafana/issues/6655)
 * **Victorops**: Add VictorOps Notification Integration [#6411](https://github.com/grafana/grafana/issues/6411)
+* **Singlestat**: New aggregation on singlestat panel [#6740](https://github.com/grafana/grafana/pull/6740)
 
 # 4.0-stable (2016-11-29)