Add videos from github webinar to "Gitting started page"

[noahsprent]

• [x] Figure out how to add videos to RTD
• [x] Add videos from Noah that are already discrete
• [ ] Decide how to trim video from webinar
• [ ] Add videos to page

[noahsprent]

@plouisross @nickdelkis I'm happy to do the actual trimming of the video down and add it to the page but could one of you take a pass over the video and decide which bits of it you want to keep as trimmed sections and what the headings can be? Take a look at https://igem-distribution.readthedocs.io/en/latest/getting_started/github.html to see what it currently looks like.

[noahsprent]

Relates to #160, #179