message: submodule check: actually check for a real file in the repo
  Git may create folders for submodules; let's make sure they're populated.
diff: <PropertyGroup>
  <ErrorText>This project references git submodule(s) that are missing on this computer. Use `git submodule update --init --recursive` to download them. For more information, see https://github.com/microsoft/terminal#building-the-code. </ErrorText>
  </PropertyGroup>
  - <Error Condition="!Exists('$(SolutionDir)\dep\wil') Or !Exists('$(SolutionDir)\dep\gsl')" Text="$([System.String]::Format('$(ErrorText)'))" />
  + <Error Condition="!Exists('$(SolutionDir)\dep\wil\README.md') Or !Exists('$(SolutionDir)\dep\gsl\README.md')" Text="$([System.String]::Format('$(ErrorText)'))" />
  </Target>
  </Project>
  