demo of using tig (a git cousin) on the oce code

I made this video for some summer students, to try to "sell them" on using git. Using the oce/R package as an example, I demonstrate how to use tig (a fast interface to git) to browse the changes in the project over the past 15 years. Fifteen years. All the changes. To folks familiar with version control, this may be "ho hum" but to newcomers used to losing their work if they drop their computer, it might be interesting :-)