Migrate "create a git repo" workshop from MigraCode Barcelona

https://syllabus.migracode.org/courses/introduction-3/course-content/introduction-2/git-and-github-practice-session has an excellent workshop on creating git repos from scratch.

Our trainees ~never create things from scratch on the course, and often get confused or stuck when we ask them to (and for many the first time they do this is final projects).

We should migrate this workshop into our workshops repo and probably set it as a coursework task at some point.