I am trying to publish NuGet with source code.
I added the source code into NuGet package like this (see right panel):

I published it to NuGet Gallery.
Then I opened Visual Studio 2013 and type this at the NuGet Package Manager Console
PM> Install-Package MySqlBackup.NET
The Package Manager Console indicated that the installation of the package was successful:

However, I found that the source code files (the .cs files) was not added into the project, only the dependency of MySql.Data was added:

What steps did I miss?
Thanks you very much for your insights.