Added link to Cloudflare exporter (#621)

* Added link to Cloudflare exporter

Featured on https://www.wehkamplabs.com/blog/2016/11/06/cloudflare-metrics-using-prometheus/

* Fixed sorting

content/docs/instrumenting/exporters.md

@@ -66,6 +66,7 @@ wide variety of JVM-based applications, for example [Kafka](http://kafka.apache.
    * [WebDriver exporter](https://github.com/mattbostock/webdriver_exporter)
 
 ### APIs
+   * [Cloudflare exporter](https://github.com/wehkamp/docker-prometheus-cloudflare-exporter)
    * [Docker Hub exporter](https://github.com/infinityworksltd/docker-hub-exporter)
    * [GitHub exporter](https://github.com/infinityworksltd/github-exporter)
    * [OpenWeatherMap exporter](https://github.com/RichiH/openweathermap_exporter)