Add glossary to the README covering at least YAML Datastore specific terms

[j-simmons-phd]

For example:

• root element
• root object
• root list
• parent element
• parent object
• parent list

Be sure to note when relationships such as all root elements are parent elements, but not all parent elements are root elements.

[j-simmons-phd]

Consider implementing as view of snippets data stored defs.