Add midonet-kubernetes to the list of 3rd party software (#1092)

Signed-off-by: YAMAMOTO Takashi <yamamoto@midokura.com>

content/docs/instrumenting/exporters.md

@@ -192,6 +192,7 @@ separate exporters are needed:
    * [Kubernetes](https://github.com/kubernetes/kubernetes) (**direct**)
    * [Linkerd](https://github.com/BuoyantIO/linkerd)
    * [mgmt](https://github.com/purpleidea/mgmt/blob/master/docs/prometheus.md)
+   * [midonet-kubernetes](https://github.com/midonet/midonet-kubernetes) (**direct**)
    * [Minio](https://github.com/minio/minio)
    * [Netdata](https://github.com/firehol/netdata)
    * [Pretix](https://pretix.eu/)
@@ -220,4 +221,4 @@ practices.
    * Java/JVM: [Hystrix metrics publisher](https://github.com/ahus1/prometheus-hystrix)
    * Java/JVM: [Jersey metrics collector](https://github.com/VitaNuova/jerseyexporter)
    * Python-Django: [django-prometheus](https://github.com/korfuri/django-prometheus)
-   * Node.js: [swagger-stats](https://github.com/slanatech/swagger-stats)
\ No newline at end of file
+   * Node.js: [swagger-stats](https://github.com/slanatech/swagger-stats)