[Docs] Add README.md for npm package #30
Description
What needs updating?
The package needs documentation for installation, basic usage e.g. for displaying on npm website https://www.npmjs.com/package/@hms-dbmi/vizarr.
Suggest using something like JSDoc (https://jsdoc.app/about-getting-started) to generate more detailed documentation for components etc. which can be hosted e.g. via gh-pages.
Where should this be updated?
https://docs.npmjs.com/about-package-readme-files A README.md can be added at the package root.
Additional context
Add any other relevant context about the documentation request.