document the `path` setting for Prometheus telemetry (#1642)
document the `path` setting for Prometheus telemetry (#1642)

#1634 didn't update the docs to reflect the new path setting for Prometheus metrics. Thanks to Amit Saha for pointing it out on Twitter.
linkerd/linkerd,BuoyantIO/linkerd,linkerd/linkerd,linkerd/linkerd,BuoyantIO/linkerd