Sass files are not added to the project, when installed bootstrap.sass nuget package

Created by: Liero

when installing bootstrap.sass into ASP.NET Core 3.1 project, the sass files are not added to the project.

The reason is described here:

package authors should use contentFiles element instead of old content element when creating packages. The author do include those files in the contentFiles folder when generating nuget packages. However, he also need to specify the contentFiles element in xx.nuspec file like this issue. Only one folder whose name is contentFiles in xx.nupkg is not enough if we want to access those files in VS Solution Explorer

Steps to reproduce:

1. Create default asp.net core project with either CLI or Visual Studio dotnet new webapp
2. cd web-app
3. Install-Package bootstrap.sass

• .NET Core 3.1
• Operating system and version Win10
• Visual Studio 16.4 (optional)