Add raw-loader

[jbccollins]

https://webpack.js.org/loaders/raw-loader/

Put it at the top of the oneOf section in webpack.config.js

oneOf: [
    // Load files as raw strings
    {
      test: [/\.txt$/, /\.md$/],
      use: 'raw-loader',
    },
    ...
]

Don't forget to document this as a change from a freshly ejected CRA!!