add docstring

Author: xrstf

pkg/metrics/registry.go

@@ -18,6 +18,8 @@ package metrics
 
 import "github.com/prometheus/client_golang/prometheus"
 
+// RegistererGatherer combines both parts of the API of a Prometheus
+// registry, both the Registerer and the Gatherer interfaces.
 type RegistererGatherer interface {
 	prometheus.Registerer
 	prometheus.Gatherer