Minor comment update

Author: walbourn

build/Directory.Build.props

@@ -1,6 +1,11 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
 
+  <!--
+      Copyright (c) Microsoft Corporation.
+      Licensed under the MIT License.
+  -->
+
   <PropertyGroup>
     <ExtractedFolder Condition="'$(ExtractedFolder)'==''">C:\xtracted\</ExtractedFolder>
     <ExtractedFolder Condition="!HasTrailingSlash('$(ExtractedFolder)')">$(ExtractedFolder)\</ExtractedFolder>