title: What purpose does the .gitignore file serve in Symfony 4?
body: <p>I have noticed that Symfony Composer automatically creates a <code>.gitignore</code> file in a new project. However, I can't find anything about a <code>.gitignore</code> file in Symfony's documentation.</p>
  
  <p>What is the purpose of this file, how does it relate to Symfony, and what should it contain?</p>