Improve the readme with an elastalert server requirement notice

Author: martijnrondeel

README.md

@@ -12,11 +12,11 @@
 ![Showcase](showcase.gif)
 
 ## Requirements
-- Our [ElastAlert](https://github.com/bitsensor/elastalert) fork
+- Our [ElastAlert server](https://github.com/bitsensor/elastalert) fork
 - Kibana 6.3.1 or higher
 
 ## Installation
-Check the [releases](https://github.com/bitsensor/elastalert-kibana-plugin/releases) page to download and install the latest version of this plugin that is compatible with your Kibana version.
+Check the [releases](https://github.com/bitsensor/elastalert-kibana-plugin/releases) page to download and install the latest version of this plugin that is compatible with your Kibana version. Please be aware that you will need a running [ElastAlert server](https://github.com/bitsensor/elastalert#installation) to make use of this plugin.
 
 ## Configuration
 By default the plugin will connect to `localhost:3030`. If your ElastAlert server is running on a different host or port add/change the following options in your `config/kibana.yml` file: