added sensu exporter (prometheus#737)

* added sensu exporter

* sorted

Author: reachlin

content/docs/instrumenting/exporters.md

@@ -110,6 +110,7 @@ wide variety of JVM-based applications, for example [Kafka](http://kafka.apache.
    * [New Relic exporter](https://github.com/jfindley/newrelic_exporter)
    * [Pingdom exporter](https://github.com/giantswarm/prometheus-pingdom-exporter)
    * [scollector exporter](https://github.com/tgulacsi/prometheus_scollector)
+   * [Sensu exporter](https://github.com/reachlin/sensu_exporter)
    * [SNMP exporter](https://github.com/prometheus/snmp_exporter) (**official**)
    * [StatsD exporter](https://github.com/prometheus/statsd_exporter) (**official**)