add drone status to readme

Author: toddtreece

README.md

@@ -1,7 +1,11 @@
+[![Build Status](https://drone.grafana.net/api/badges/grafana/mqtt-datasource/status.svg?ref=refs/heads/main)](https://drone.grafana.net/grafana/mqtt-datasource)
+
 # MQTT data source for Grafana
 
 The MQTT data source plugin allows you to visualize streaming MQTT data from within Grafana.
 
+![mqtt dashboard](./test_broker.js)
+
 ## Requirements
 
 The MQTT data source has the following requirements: