add a section to metrics doc on how to scrape
This change adds a paragraph and example at the beginning of the metrics
doc describing how to performa a manual scrape on the prometheus port.
This is being added to help developers understand how to interact with
metrics directly.
# MAO Metrics
+The Machine API Operator(MAO) uses the
+[Prometheus project](https://prometheus.io/) to expose metrics. To consume
+these metrics directly from the MAO you will need to perform
+HTTP GET requests to a specific port and URI of the MAO. The
+URI for all metrics is `/metrics`, see the Prometheus documentation for query
+parameter options. To find the exposed metrics port for the MAO you can either
+inspect the Deployment resource or the
+[install manifest](https://github.com/openshift/machine-api-operator/blob/master/install/0000_30_machine-api-operator_11_deployment.yaml)
+to find the environment variable `METRICS_PORT`, the default value for this is `8080`.
+
+**Example MAO metrics scrape procedure**
+1. Forward the metrics port from the CAO to a local port
+ ```
+ $ oc port-forward -n openshift-machine-api deployment/machine-api-operator 8080:8080
+ ```
+2. Perform an HTTP GET request on the local port
+ ```
+ $ curl http://localhost:8080/metrics
+ ```
+
The Machine API Operator reports the following metrics:
## Metrics about Machine resources
