title: command 'vagrant box add' fail
body: <p><a href="http://docs.vagrantup.com/v2/getting-started/boxes.html" rel="noreferrer">vagrantup.com</a> says input <code>vagrant box add hashicorp/precise32</code>, <br><br>But when I input it, the terminal outputs error message:</p>
  
  <pre><code>This command was not invoked properly. The help for this command is
  available below.
  
  Usage: vagrant box add &lt;name&gt; &lt;url&gt; [--provider provider] [-h]
  </code></pre>
  
  <p>Then, I input <code>vagrant box add hashicorp/precise32 \ http://files.vagrantup.com/hashicorp/precise32.box</code>, <br>
  But the download fail, with following error message.<br></p>
  
  <pre><code>Download failed. Will try another box URL if there is one.
  An error occurred while downloading the remote file. The error
  message, if any, is reproduced below. Please fix this error and try
  again.
  
  Couldn't open file /Users/XXXX/ http:/files.vagrantup.com/precise32.box
  </code></pre>
  
  <p>How do I do to install vagrant box?</p>