yarn add skynet-js
src/App.js, look for where Step 1.2 code goes, and paste the following code.
handleSubmitfunction (which is called when the form is submitted), paste the code that will upload a file to Skynet below the Step 1.3 mark.
yarn startagain and try uploading a file. If you open your Developer Console (by pressing F12), the console will show helpful messages about what the code is doing.