Update README.md

Adding OMD which is a nice tool to setup a nagios-based monitoring environment including most of the ecosystem tools with sane default configuration and a well thought out workflow tools for the commandline.

README.md

@@ -163,6 +163,7 @@ A curated list of amazingly awesome open source sysadmin resources inspired by [
 * [Naemon](http://www.naemon.org/) - Network monitoring tool based on the Nagios 4 core with performance enhancements and new features.
 * [Nagios](http://www.nagios.org/) - Computer system, network and infrastructure monitoring software application.
 * [Observium](http://www.observium.org/) - SNMP monitoring for servers and networking devices. Runs on linux.
+* [OMD](http://omdistro.org/) - OMD - The Open Monitoring Distribution
 * [Opsview](http://www.opsview.com/solutions/core) - Based on Nagios 4, Opsview Core is ideal for small IT and test environments.
 * [Riemann](http://riemann.io/) - Flexible and fast events processor allowing complex events/metrics analysis.
 * [Sensu](http://sensuapp.org/) - Open source monitoring framework.