Adding AL 2.0 header to checkstyle.xml to satisfy RAT

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/cli/branches/cli-1.x@741420 13f79535-47bb-0310-9956-ffa450edef68

Author: hen

src/conf/checkstyle.xml

@@ -1,4 +1,21 @@
 <?xml version="1.0"?>
+<!--
+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.
+-->
+
 <!DOCTYPE module PUBLIC
     "-//Puppy Crawl//DTD Check Configuration 1.1//EN"
     "http://www.puppycrawl.com/dtds/configuration_1_1.dtd">