Update the README

Author: Timer

packages/react-error-overlay/README.md

@@ -1,7 +1,11 @@
 # `react-error-overlay`
 
-An overlay for displaying stack frames.
+`react-error-overlay` is an overlay which displays when there is a runtime error.
 
-# API
+## Development
 
-<!-- Generated by documentation.js. Update this documentation by updating the source code. -->
+When developing within this package, make sure you run `npm start` (or `yarn start`) so that the files are compiled as you work.
+This is ran in watch mode by default.
+
+If you would like to build this for production, run `npm run build:prod` (or `yarn build:prod`).<br>
+If you would like to build this one-off for development, you can run `NODE_ENV=development npm run build` (or `NODE_ENV=development yarn build`).