add review comment to sb files (#48566)

* add review comment to sb files

* add CODEOWNERS entry for source-build

.github/CODEOWNERS

@@ -16,6 +16,7 @@
 /eng/common/                                                                      @dotnet-maestro-bot
 /eng/Versions.props                                                               @dotnet-maestro-bot @dotnet/aspnet-build @wtgodbe
 /eng/Version.Details.xml                                                          @dotnet-maestro-bot @dotnet/aspnet-build @wtgodbe
+/eng/SourceBuild*                                                                 @dotnet/source-build-internal
 /src/Caching/                                                                     @captainsafia @halter73 @mgravell
 /src/Caching/**/PublicAPI.*Shipped.txt                                            @dotnet/aspnet-api-review @captainsafia @halter73 @mgravell
 /src/Components/                                                                  @dotnet/aspnet-blazor-eng

eng/SourceBuild.props

@@ -1,3 +1,5 @@
+<!-- Whenever altering this or other Source Build files, please include @dotnet/source-build-internal as a reviewer. -->
+
 <Project>
 
   <PropertyGroup>

eng/SourceBuildPrebuiltBaseline.xml

@@ -1,3 +1,6 @@
+<!-- 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.*/*" />