feat(changelog): add info about merge PR to changelog

CHANGELOG.md

@@ -4,6 +4,7 @@
 * **Elasticsearch**: Support for pipeline aggregations Moving average and derivative, closes [#2715](https://github.com/grafana/grafana/issues/2715)
 * **Syslog**: Support for syslog logging, closes [#3161](https://github.com/grafana/grafana/pull/3161)
 * **Timepicker**: Always show refresh button even with refresh rate, closes [#3498](https://github.com/grafana/grafana/pull/3498)
+* **Login**: Make it possible to change the login hint on the login page, closes [#2571](https://github.com/grafana/grafana/pull/2571)
 
 ### Bug Fixes
 * **metric editors**: Fix for clicking typeahead auto dropdown option, fixes [#3428](https://github.com/grafana/grafana/issues/3428)