doc: Add reference to gnocchi-nagios tool

Change-Id: Iaabf427c948fa1bd095d374f1ca2bc8fda628bac

doc/source/index.rst

@@ -50,6 +50,7 @@ Key Features
 - Queryable resource indexer
 - Multi-tenant
 - Grafana support
+- Nagios/Icinga support
 - Statsd protocol support
 
 
@@ -67,6 +68,7 @@ Documentation
    rest
    statsd
    grafana
+   nagios
    glossary
    releasenotes/index.rst
 

doc/source/nagios.rst

@@ -0,0 +1,19 @@
+=====================
+Nagios/Icinga support
+=====================
+
+`Nagios`_ and `Icinga`_ has support for Gnocchi through a Gnocchi-nagios
+service. It can be installed with pip::
+
+     pip install gnocchi-nagios
+
+`Source`_ and `Documentation`_ are also available.
+
+Gnocchi-nagios collects perfdata files generated by `Nagios`_ or `Icinga`_;
+transforms them into Gnocchi resources, metrics and measures format; and
+publishes them to the Gnocchi REST API.
+
+.. _`Nagios`: https://www.nagios.org/
+.. _`Icinga`: https://www.icinga.com/
+.. _`Documentation`: http://gnocchi-nagios.readthedocs.io/en/latest/
+.. _`Source`: https://github.com/sileht/gnocchi-nagios