Fixes for unhandled error events on npm start to Readme

[TimMcCauley]

https://github.com/gatsbyjs/gatsby/issues/1767 & https://stackoverflow.com/questions/22475849/node-js-what-is-enospc-error-and-how-to-solve

echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf && sudo sysctl -p