feat(plugins): updated changelog with notice about plugin api changes

CHANGELOG.md

@@ -5,6 +5,7 @@
 * **Metadata**: Settings panel now shows dashboard metadata, closes [#3304](https://github.com/grafana/grafana/issues/3304)
 
 ### Breaking changes
+**Plugin API**: Both datasource and panel plugin api (and plugin.json schema) as been updated, requiring a minor update to plugins. See [plugin api](https://github.com/grafana/grafana/blob/master/public/app/plugins/plugin_api.md) for more info.
 **InfluxDB 0.8.x** The data source for the old version of influxdb (0.8.x) is no longer included in default builds. Can easily be installed via improved plugin system, closes #3523
 **KairosDB** The data source is no longer included in default builds. Can easily be installed via improved plugin system, closes #3524