Add exporter for App Connect Enterprise (#1238)

* Add exporter for App Connect Enterprise

App Connect Enterprise is an integration product (formally known as IBM Integration Bus or WebSphere Message Broker)

The exporter is available at https://github.com/ot4i/ace-docker and further work is planned to de-couple from this repository so it can be more readily included in projects
Signed-off-by: Martin Ross <martin.ross@uk.ibm.com>

content/docs/instrumenting/exporters.md

@@ -188,6 +188,7 @@ possible.
 Some third-party software exposes metrics in the Prometheus format, so no
 separate exporters are needed:
 
+   * [App Connect Enterprise](https://github.com/ot4i/ace-docker)
    * [Ballerina](https://ballerina.io/)
    * [Ceph](http://docs.ceph.com/docs/master/mgr/prometheus/)
    * [Collectd](https://collectd.org/wiki/index.php/Plugin:Write_Prometheus)