Add Webpacker

Most of this is automatically generated by the rake task: `bundle exec rake webpacker:install`

Docs: https://github.com/rails/webpacker/tree/5-x-stable

app/javascript/packs/application.js

@@ -0,0 +1,18 @@
+/* eslint no-console:0 */
+// This file is automatically compiled by Webpack, along with any other files
+// present in this directory. You're encouraged to place your actual application logic in
+// a relevant structure within app/javascript and only use these pack files to reference
+// that code so it'll be compiled.
+//
+// To reference this file, add <%= javascript_pack_tag 'application' %> to the appropriate
+// layout file, like app/views/layouts/application.html.erb
+
+
+// Uncomment to copy all static images under ../images to the output folder and reference
+// them with the image_pack_tag helper in views (e.g <%= image_pack_tag 'rails.png' %>)
+// or the `imagePath` JavaScript helper below.
+//
+// const images = require.context('../images', true)
+// const imagePath = (name) => images(name, true)
+
+console.log('Hello World from Webpacker')