Add NuGet Package README file for EFcore #30467
Description
Issue:
Currently, there is no README file for EF Core package. for example: https://www.nuget.org/packages/Microsoft.EntityFrameworkCore.SqlServer/8.0.0-preview.1.23111.4
Action:
Add NuGet README file so that it will be easier for users to get started with know about the EF core packages.