changelog(): added entry for PR grafana#6579

Author: torkelo

CHANGELOG.md

@@ -10,6 +10,7 @@
 ### Enhancements
 * **Singlestat**: Support repeated template variables in prefix/postfix [#6595](https://github.com/grafana/grafana/issues/6595)
 * **Templating**: Don't persist variable options with refresh option [#6586](https://github.com/grafana/grafana/issues/6586)
+* **Alerting**: Add ability to have OR conditions (and mixing AND & OR) [#6579](https://github.com/grafana/grafana/issues/6579)
 
 # 4.0-beta1 (2016-11-09)