title: create-react-app uses modules despite not showing in package.json
body: <p>From what I understand the <code>create-react-app</code> command installs all we need to get started, and more. I am currently trying to get ESLint AirBnB &amp; Prettier to work, and eslint needs quite a few dependencies.</p>
  
  <p>When browsing my <code>node_modules</code>, I noticed that <code>eslint-config-airbnb</code> AND <code>eslint-config-airbnb-base</code> were listed. In <code>package.json</code> I have <code>"eslint-config-airbnb": "^17.1.0",</code> listed <strong>only</strong>.</p>
  
  <p>Correct me if I'm wrong, but my assumption now is that all those packages which have peer dependencies still work fine with each other despite not all being listed in package.json. Is this based on <code>create-react-app</code> hiding most of the config from us? Any additional input you can give me about the topic?</p>
  
  <p>The above modules and dependencies are really just representative of the theoretical question as a whole. I am using eslint config as an example.</p>
  
  <p>Cheers</p>
  
  <p>EDIT: I used the eslint example because I actually did have an issue with it not loading correctly, nor linting correctly. I fixed the issue by moving the <code>.eslintrrc.js</code> out of the project directory, and into the parent directory. Why this works, I have no idea </p>