Overlays

TODO: Starter content. This content still needs to be written.

• what is an overlay
• to consider: WP plugins for overlays and their claim (maybe not) .
• the difference between an overlay and a toolbar.
• link to overlayfactsheet.com
• include video Overlays Underwhelm by Adrian Roselli.
• include video Overlays Underwhelm by Léoni Watson.
• add more resources from within the WP community.