Adding a service worker to a React Static and Netlify CMS website

I've recently launched my new [portfolio](https://www.jamessidhu.com) using React Static with a blog powered by [Netlify CMS](https://netlifycms.org). One of the first performance improvements is adding a service worker to improve the time of rendering and performance between navigating the pages. You won't find a service worker included in React Static because of edge cases, which requires customisations for different types of application, but it's a simple task to do when you draw from the concepts from universal and progressive web applications.