title: How to add non-public repositories from command line with composer?
body: <p>I want to add a new package which is not at packagist, it's a local or non-public repository. I know how to this in the <code>composer.json</code>. For example:</p>
  
  <pre><code>"repositories": [
      {
          "type": "vcs",
          "url": "https://bitbucket.org/xxxx/xxxxx.git"
      }
  ],
  "require": {
      "xxxx/xxxxx": "dev-master"
  },
  </code></pre>
  
  <p>But I want to do this from the command line so that I can add this non-public repositories in a provision file.
  Packages registered at Packagist I can add with:</p>
  
  <pre><code>composer require ....
  </code></pre>
  
  <p>But how to handle this with repositories not registered at Packagist?</p>