Improve "Introduction to Git and GitHub" presentation

[justmarkham]

Items already modified from original presentation:

• remove some of the introductory exposition
• make many slides less wordy
• remove unnecessary points/side notes and combine slides when possible
• add points to address things that were confusing to students
• highlight all commands in red so they are easier to identify
• add a "recap" slide midway through the presentation
• use the Dropbox metaphor throughout the presentation
• reorder some slides

Possible improvements to consider:

• Instead of (or in addition to) some of the slides, give students a heavily-annotated "script" with all of the commands so that they can follow along even if they get behind. (The script can also serve as a reminder later on when they forget what certain commands do.)
• Add another workflow diagram, perhaps early in the presentation
• More explanation on SSH, and more detailed instructions for setting up SSH
• Add more detail to the "recipe"
• Add transition slides to make it more clear where you are in the presentation, and perhaps name or number the exercises

Other suggestions welcome!

[ajschumacher]

feel free to move the possible improvements to the issue system!

[ajschumacher]

Oops! Misread; thought I was looking at a commit message. :)