router.sh is missing in Druid Distribution (apache#15547)

Every time we roll out a new version of Druid on our cluster, I recognize that the script for starting the router process is missing. So I added it =)

examples/bin/router.sh

@@ -0,0 +1,25 @@
+#!/bin/bash -eu
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You 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.
+
+usage="Usage: router.sh (start|stop|status)"
+
+if [ $# -lt 1 ]; then
+  echo $usage
+  exit 1
+fi
+
+cd $(dirname $0)/../
+sh ./bin/node.sh router $1