add nagios fork icinga to monitoring tools

README.md

@@ -200,6 +200,7 @@ CMS are a practical way to setup a website with many features. CMS often come wi
 
 ## Monitoring and administration
 
+  * [Icinga / Icinga 2](https://www.icinga.org/) - Nagios fork that has since lapped nagios several times. Comes with the possibility of clustered monitoring - ([SourceCode](https://github.com/Icinga)) - `GPLv2`
   * [linux-dash](https://github.com/afaqurk/linux-dash) - A drop-in, low-overhead monitoring web dashboard for a linux machine ([Demo](http://afaq.dreamhosters.com/linux-dash/))
   * [Nagios](https://www.nagios.org/) - Industry standard monitoring software, which has a lot of plugins and customisation posibilities. - `GPL`
   * [psdash](https://github.com/Jahaja/psdash) - A linux system information web dashboard using psutils and flask