How I add a .shproj to my Visual Studio solution and reference it from other projects?

I know that Visual Studio 2013 Update 2 added a new project type for "Shared Code." This type of project does not produce a dll itself. Instead the files from the Shared project are included as source files in the assemblies that reference it.
I know it exists because I have seen one in an open source project. However, looking through the project templates in Visual Studio I could not find a "Shared" project type.