[Docs]: Instruct users to do EnableMSTestRunner in Directory.Build.props and not in csproj

[Youssef1313]

Adding this property to csproj can easily cause users to fall in hybrid mode. The docs should advise to add it in Directory.Build.props at repo root. The property should be having zero effect for non-test projects so it's fine to be in Directory.Build.props in repo root if users are not separating src and tests directories.
If they are separating, I think it doesn't matter that much to be in <RepoRoot>/Directory.Build.props or <RepoRoot>/tests/Directory.Build.props.

[Youssef1313]

This is going to be a bit tricky considering what we want to do for templates though 😕

[Evangelink]

I am strongly starting to think it might be good to introduce a separate package that is new platform only so we could drop lots of deps to old world and drop all these properties because you would be in new world by default.

@MarcoRossignoli the time has come for our baby to fly 😆

[MarcoRossignoli]

I am strongly starting to think it might be good to introduce a separate package that is new platform only so we could drop lots of deps to old world and drop all these properties because you would be in new world by default.

Well the SDK...if "well supported everywhere" would be "that", with the time to "cut" what we don't want and refactor the packaging.