It means if you do start a GitHub, you can configure it to work with Shakespeare to backup your code. Then if you DO use Shakespeare to build something ever, it will automatically back up your code as you build.

You can use Shakespeare w/o GitHub. You can use GitHub without Shakespeare.

Git = version control.

Just means you have a way to back up code & share with others, rollback to the last version when you screw something up in whatever you're using—Shakespeare or any other building tool.