add documentation for prometheus config option

website/source/api/metrics.html.md

@@ -22,12 +22,22 @@ The table below shows this endpoint's support for
 | ---------------- | ------------ |
 | `NO`             | `none`       |
 
+### Parameters
+
+- `format` `(string: "")` - Specifies the metrics format to be other than the
+  JSON default. Currently, only `prometheus` is supported as an alterntaive
+  format. This is specified as a querystring parameter.
+
 ### Sample Request
 
 ```text
 $ curl https://nomad.rocks/v1/metrics
 ```
 
+```text
+$ curl https://nomad.rocks/v1/metrics?format=prometheus
+```
+
 ### Sample Response
 
 ```json

website/source/docs/agent/configuration/telemetry.html.md

@@ -114,6 +114,15 @@ telemetry {
 }
 ```
 
+### `prometheus`
+
+These `telemetry` parameters apply to
+[Prometheus](https://prometheus.io).
+
+- `prometheus_metrics` `(bool: false)` - Specifies whether the agent should
+  initialize a PrometheusSink, where metrics will be reachable via the metrics
+  path `/v1/netrics?format=prometheus`.
+
 ### `circonus`
 
 These `telemetry` parameters apply to