Add a few comments and add the property to the static lib project template.

Author: jlaanstra

nuget/Microsoft.Windows.CppWinRT.targets

@@ -117,6 +117,7 @@ Copyright (C) Microsoft Corporation. All rights reserved.
         </ItemGroup>
     </Target>
 
+    <!-- Target used only to evaluate CppWinRTGenerateWindowsMetadata if it doesn't already have a value -->
     <Target Name="ComputeCppWinRTResolvedWinMD"
             Condition="'$(CppWinRTGenerateWindowsMetadata)' == ''"
             DependsOnTargets="GetCppWinRTMdMergeInputs">
@@ -419,6 +420,7 @@ $(XamlMetaDataProviderPch)
     </Target>
 
     <!-- Only copy winmd to output folder if CppWinRTGenerateWindowsMetadata is true -->
+    <!-- Note that Condition is evaluated before DependsOnTargets are run -->
     <Target Name="CppWinRTResolvedWinMDToOutputDirectory"
             Condition="'$(CppWinRTGenerateWindowsMetadata)' == 'true'"
             DependsOnTargets="CppWinRTMergeProjectWinMDInputs;$(CppWinRTResolvedWinMDToOutputDirectoryDependsOn)"

vsix/ProjectTemplates/VC/Windows Universal/StaticLibrary/StaticLibrary.vcxproj

@@ -3,6 +3,7 @@
   <PropertyGroup Label="Globals">
     <CppWinRTOptimized>true</CppWinRTOptimized>
     <CppWinRTRootNamespaceAutoMerge>true</CppWinRTRootNamespaceAutoMerge>
+    <CppWinRTGenerateWindowsMetadata>true</CppWinRTGenerateWindowsMetadata>
     <CppWinRTParameters>-lib $(MSBuildProjectName)</CppWinRTParameters>
     <MinimalCoreWin>true</MinimalCoreWin>
     <ProjectGuid>{$guid1$}</ProjectGuid>