add review comment to sb files (#8787)

* add review comment to sb files

* add CODEOWNERS entry for source-build

.github/CODEOWNERS

@@ -7,6 +7,7 @@
 /eng/common/                                   @dotnet/razor-tooling @dotnet/razor-compiler
 /eng/Versions.props                            @dotnet/razor-tooling @dotnet/razor-compiler
 /eng/Version.Details.xml                       @dotnet/razor-tooling @dotnet/razor-compiler
+/eng/SourceBuild*                              @dotnet/source-build-internal
 /src/Razor                                     @dotnet/razor-tooling
 /src/Compiler                                  @dotnet/razor-compiler
 /src/Shared                                    @dotnet/razor-tooling @dotnet/razor-compiler

eng/SourceBuild.props

@@ -1,4 +1,6 @@
-<Project>
+<!-- Whenever altering this or other Source Build files, please include @dotnet/source-build-internal as a reviewer. -->
+
+<Project>
   <PropertyGroup>
     <GitHubRepositoryName>razor</GitHubRepositoryName>
     <SourceBuildManagedOnly>true</SourceBuildManagedOnly>

eng/SourceBuildPrebuiltBaseline.xml

@@ -1,4 +1,7 @@
-<UsageData>
+<!-- Whenever altering this or other Source Build files, please include @dotnet/source-build-internal as a reviewer. -->
+<!-- See aka.ms/dotnet/prebuilts for guidance on what pre-builts are and how to eliminate them. -->
+
+<UsageData>
   <IgnorePatterns>
     <UsagePattern IdentityGlob="Microsoft.SourceBuild.Intermediate.*/*" />