TFS looks inside the .csproj files and the different service reference files to see which files need to be added to source control when you do the "Add solution to Sourcecontrol" step.
What I usually do is that I map the folder where my solution is located and then in the Source Control window use the Add files and folders button to add the files to sourcecontrol manually.
Then open the solution by doubleclicking the sln
file directly in the Source Control Explorer and then when prompted, agree that Visual Studio updates the source control bindings for you.