Improve ReadMe

The ReadMe for this project is a little bare-bones. While we have a documentation site, it would be nice to include some more information explaining why the project exists and how it is useful.

Since DS-CLI is basically a Create React App for design systems, I think some of the elements of the [CRA](https://github.com/facebook/create-react-app) readme would be good to include.

Installation guide, video setting up a new design system, philosophy, features etc would all be useful. We really should hammer that setting up all of the monorepo, Storybook, and build tools takes over a week if you piece it together yourself. You can do it with this project in minutes.