modify images in readme

[hbeale]

I incorporated images from some slides into the readme. I think they are useful but could use so improvement.

• The titles of the slides are large in size and make it hard to visually follow the headers in the readme.
• The numbering isn't used elsewhere; consider removing it
• It might also be beneficial to change the text of the slide titles.
• It might be useful to refer to the slides in the readme text

The editable slides are here: https://docs.google.com/presentation/d/1UBoChUf2FTN1wMm1Znzo6Xzglo1UniiepaIw-q0PxfQ/edit?usp=sharing