Add readme.md into the Kitfile / ModelKit

[bmicklea]

Describe the problem your feature would solve
It can sometimes be difficult to understand what a model is meant to be used for and what datasets are / why they were included.

Describe the solution you'd like
A readme included in the ModelKit would make it easy for the Kitfile producer and consumer to understand the context for the ModelKit and the assets it is packaging.

Describe alternatives you've considered
Descriptions in the Kitfile are okay, but are either very short and keep the Kitfile readable, or are very long and wreck the readability.

Additional context
[none]