Add missing instrumentation.go file to Git.

Change-Id: I073511190b9e279ff2a01b92d3a466e9e8778b2f

config/instrumentation.go

@@ -0,0 +1,24 @@
+// Copyright 2013 Prometheus Team
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package config
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var configLoads = prometheus.NewCounter()
+
+func init() {
+	prometheus.Register("alertmanager_config_reloads_total", "The number of configuration reloads.", prometheus.NilLabels, configLoads)
+}