Add production disclaimer

Author: marcusolsson

README.md

@@ -5,6 +5,8 @@
 
 A data source plugin for loading JSON APIs into [Grafana](https://grafana.com).
 
+**Important:** This plugin is **not** production-ready yet. In the meantime, try it out and [submit an issue](https://github.com/marcusolsson/grafana-jsonapi-datasource/issues/new) for bug reports and feature requests.
+
 ![Screenshot](https://raw.githubusercontent.com/marcusolsson/grafana-jsonapi-datasource/master/src/img/screenshot.png)
 
 Extract one or more values from a JSON API using [JSON Path](https://goessner.net/articles/JsonPath/). Each path results in a field in the query result. All fields need to be of the same length.