docs(changelog): add opentsdb annotations to changelog

CHANGELOG.md

@@ -25,6 +25,7 @@
 * **graph**: Template variables can now be used in TimeShift and TimeFrom, closes[#1960](https://github.com/grafana/grafana/issues/1960)
 * **Tooltip**: Optionally add milliseconds to timestamp in tool tip, closes[#2248](https://github.com/grafana/grafana/issues/2248)
 * **Opentsdb**: Support milliseconds when using openTSDB datasource, closes [#2865](https://github.com/grafana/grafana/issues/2865)
+* **Opentsdb**: Add support for annotations, closes[#664](https://github.com/grafana/grafana/issues/664)
 
 ### Bug fixes
 * **Playlist**: Fix for memory leak when running a playlist, closes [#3794](https://github.com/grafana/grafana/pull/3794)