docs(changelog): add note about solving sync problem for alerts

CHANGELOG.md

@@ -5,6 +5,7 @@
 * **Graph panel**: Fixed graph panel tooltip sort order issue [#6648](https://github.com/grafana/grafana/issues/6648)
 * **Unsaved changes**: You now navigate to the intended page after saving in the unsaved changes dialog [#6675](https://github.com/grafana/grafana/issues/6675)
 * **TLS Client Auth**: Support for TLS client authentication for datasource proxies [#2316](https://github.com/grafana/grafana/issues/2316)
+* **Alerts out of sync**: Saving dashboards with broken alerts causes sync problem[#6576](https://github.com/grafana/grafana/issues/6576)
 
 # 4.0-beta2 (2016-11-21)