docs(changelog): add note about updating systemd description

CHANGELOG.md

@@ -11,6 +11,9 @@
 * **Graphite**: Add support for groupByNode, closes [#5613](https://github.com/grafana/grafana/pull/5613)
 * **Influxdb**: Add support for elapsed(), closes [#5827](https://github.com/grafana/grafana/pull/5827)
 
+### Breaking changes
+* **SystemD**: Change systemd description, closes [#5971](https://github.com/grafana/grafana/pull/5971)
+
 # 3.1.2 (unreleased)
 * **Templating**: Fixed issue when combining row & panel repeats, fixes [#5790](https://github.com/grafana/grafana/issues/5790)
 * **Drag&Drop**: Fixed issue with drag and drop in latest Chrome(51+), fixes [#5767](https://github.com/grafana/grafana/issues/5767)