Add visualization for comparing equity and equality (and image licensing)

There is a great visualization that helps to show the difference between equity and equality:


(source: https://www.flickr.com/photos/communityeyehealth/27755848262)

There exist several derivatives of this image and every time I am teaching the instructor training somebody is pointing to one of them. :) I think it would make to include one of them to make the abstract difference easier to grasp. The images linked aboce seems to be under a CC-BY-NC license so reuse would be possible.

Locate the instructor-training lesson section where the equity and equality distinction is taught, then review the linked Flickr image and its derivatives for licensing and attribution requirements. Done means an appropriate visualization is included with clear source and license attribution, without creating reuse concerns.

Written by the indexing model from the issue text.