Add a cheat sheet/overview section to the wiki

[essvee]

Notes from review meeting: 2022-07-28

Needs to function as a walk-thru/overview of basics and help a new reader understand the function of the different parts of the standard (termlist, wiki, termlist header), how they should be read and how they work together.

Examples:

• https://ogcapi.ogc.org/common/overview.html
• https://iiif.io/get-started/how-iiif-works/
• https://www.w3.org/TR/annotation-model/