Hi!
To import your project into source control, you first need to import it with a dedicated tool.
For instance, the creation of the Git project can be done in command line with the “git init” inside your project directory.
See https://answers.unrealengine.com/questions/190819/source-control-error-project-is-not-part-of-a-git.html
Also, my git plugin was not working with Mac in 4.7.x, see for instance:
https://answers.unrealengine.com/questions/180455/trouble-setting-up-bitbucket-source-control-471.html
There is also a wiki tutorial:
Let me know if this help!
Cheers!