[DOCS] Add Keith's SDK video to our documentation

[aaronreed708]

Problem/Concern

The final video that Keith did for us to introduce the concepts of the Theme Builder SDK has been posted to the FINOS YouTube channel and can be found here: https://www.youtube.com/watch?v=g9JVOudI5K8&list=PLmPXh6nBuhJvYfhZgdb3LqImhOn5r7Dp_. This issue is to add this link to our documentation where it makes sense.

Proposed Solution

I suggest that this video:

• be listed as a resource in our mkdocs documentation
• be added to the Theme Builder SDK README as an introductory video.
  • or would this be better added to the developer doc