Create documentation on the internals and design of Microkit

[Ivan-Velickovic]

It is important to outline the philosophy and goals of Microkit in a transparent way. This has been partially done in various places, but not in any single central place like this repository.

This documentation should contain the general goals as well as an overview of the design of Microkit and all the components that make up Microkit (e.g loader, initial task, libmicrokit).