Add comment describing what this thing can do

This is somewhat preliminay, having only a Repository and Commit object
may not be enough for this project. We could add some other things such
as Remote objects and Tree objects.
Add factory methods for crating the repositories
Call the init:(NSString) 'clone' instead
Include repository location for init/clone
Add method to add files to a repository
Move the implementation into the .m file
Allow relative file path for addFile
Add method to reset the stating index
Add method to get the status of the repository