Improve documentation and add badges

Author: martijnrondeel

README.md

@@ -2,10 +2,15 @@
 
 > This plugin provides a way to create, test and edit ElastAlert rules within Kibana.
 
-![Showcase](showcase.gif)
+![GitHub release](https://img.shields.io/github/release/bitsensor/elastalert-kibana-plugin.svg)
+![Github Releases](https://img.shields.io/github/downloads/bitsensor/elastalert-kibana-plugin/total.svg)
+![GitHub stars](https://img.shields.io/github/stars/bitsensor/elastalert-kibana-plugin.svg?style=social&label=Stars)
 
 ---
 
+## Demo
+![Showcase](showcase.gif)
+
 ## Requirements
 - Our [ElastAlert](https://github.com/bitsensor/elastalert) fork
 - Kibana 6.3.1 or higher