Resources: add Sam M video on Git

[reshamas]

Folder:
https://github.com/reshamas/git-intro-workshop/tree/master/extra_resources

Video:
https://youtu.be/edCiPBn_dj8

Note: can create a new Markdown file, call it video-tutorials.md

[reshamas]

@RandalSchwartz is working on this as an example for a presentation.