The rules say:
"Create a new public GitHub repository to store the source code and any assets you’re able to share for your entry and push your changes before December 1 13:37 PT."
So, if you have assets that you can't share (e.g. because you're bought them and aren't allowed to redistribute them outside of your game), you don't need to add them to the repository. But if you *can* share them, my read is that you need to do so,