Add sabnzbd exporter to docs (#933)

content/docs/instrumenting/exporters.md

@@ -143,6 +143,7 @@ wide variety of JVM-based applications, for example [Kafka](http://kafka.apache.
    * [PowerDNS exporter](https://github.com/ledgr/powerdns_exporter)
    * [Process exporter](https://github.com/ncabatoff/process-exporter)
    * [rTorrent exporter](https://github.com/mdlayher/rtorrent_exporter)
+   * [SABnzbd exporter](https://github.com/msroest/sabnzbd_exporter)
    * [Script exporter](https://github.com/adhocteam/script_exporter)
    * [Shield exporter](https://github.com/cloudfoundry-community/shield_exporter)
    * [SMTP/Maildir MDA blackbox prober](https://github.com/cherti/mailexporter)
@@ -150,6 +151,7 @@ wide variety of JVM-based applications, for example [Kafka](http://kafka.apache.
    * [Unbound exporter](https://github.com/kumina/unbound_exporter)
    * [Xen exporter](https://github.com/lovoo/xenstats_exporter)
    
+
 When implementing a new Prometheus exporter, please follow the
 [guidelines on writing exporters](/docs/instrumenting/writing_exporters)
 Please also consider consulting the [development mailing