Port Git Internals deck to HydeSlides format

[jordanmccullough]

As discussed in #233, the Git Internals deck should be converted to HydeSlides format (i.e. Markdown).

[matthewmccullough]

No rush, but this would be great. This talk has been going over wonderfully in Training Team conversation.

[tlberglund]

I give this talk frequently, and do it all from Foundations diagrams and live-coded examples. I would definitely use moar illustrations if they existed, and being able to link students to a deck afterwards would be suhweet. Whenever you get to it, @jordanmccullough, this would be sooper. :)