Investigate result of XProj to CSProj migration for nuget.exe

[emgarten]

Scenario

1. Migrate a large XProj solution to CSProj PackageReference.
2. build.ps1 and build.sh scripts that were previously working by running nuget.exe restore <root dir> now no longer work since recursive project.json search has been removed.

Expectation

NuGet should provide guidance on the best way to migrate scripts that were relying on recursive directory and direct project.json restore for the new MSBuild based system.

As part of this some real world customer repositories should be looked at to see what would be needed to update their build scripts to work after migration.

[emgarten]

This is a doc issue

[jainaashish]

Closing it here since we're tracking it in docs repo