Link specific parts of the git_basics livestream to every appropriate section of the web site.

- Add a link (with the timestamp of the appropriate section) of the [git_basics livestream](https://www.youtube.com/watch?v=HF12-91iazM) to the top of the appropriate section of the web site.
- All the topics and commands covered in the livestream are listed in the description of the video.
- On YouTube, click on 'share' and copy the link after checking the 'start at' checkbox (ensure that the correct timestamp for that section is entered in the input).

Eg: Add **'Watch a short video on [git pull](https://youtu.be/HF12-91iazM?t=3789).'** to the top of the `git pull` sub-section of the web site.