Merge pull request #351 from mdlayher/master

Add rTorrent third party exporter

content/docs/instrumenting/exporters.md

@@ -66,6 +66,7 @@ hosted outside of the Prometheus GitHub organization.
    * [Redis exporter](https://github.com/oliver006/redis_exporter)
    * [RethinkDB exporter](https://github.com/oliver006/rethinkdb_exporter)
    * [Rsyslog exporter](https://github.com/digitalocean/rsyslog_exporter)
+   * [rTorrent exporter](https://github.com/mdlayher/rtorrent_exporter)
    * [scollector exporter](https://github.com/tgulacsi/prometheus_scollector)
    * [SMTP/Maildir MDA blackbox prober](https://github.com/cherti/mailexporter)
    * [Speedtest.net exporter](https://github.com/RichiH/speedtest_exporter)