title: No such file or directory - when running git add
body: <p>I'm going to upload my code to the github repository and execute the <code>git add .</code> command. I get this error and I do not know what to do in this case.</p>
  
  <pre><code>fatal: Unable to create '/Documents/GitHub/repo/.git/index.lock': No such file or directory
  </code></pre>