changelog: adds note about closing #15651

CHANGELOG.md

@@ -1,3 +1,8 @@
+# 6.0.1 (unreleased)
+
+### Bug Fixes
+* **Metrics**: Fixes broken usagestats metrics for /metrics [#15651](https://github.com/grafana/grafana/issues/15651)
+
 # 6.0.0 stable (2019-02-25)
 
 ### Bug Fixes