title: Is there a solution for required mutually exclusive arguments listed as optional in help section?
body: <p>So using argparse I created a mutually exclusive group which has two items. One of the must be always passed, so I created the group with <code>required=True</code>.</p>
  
  <p>It's properly working, If I don't call the script with either of them, it will fail with <code>error: one of the arguments --foo --bar is required</code></p>
  
  <p>However, the problem comes when I just run it with <code>-h</code> or <code>--help</code>. It's listing these parameters as optional, but they are not. </p>
  
  <pre><code>optional arguments:
    -h, --help            show this help message and exit
    --foo                 foo
    --bar                 bar
  
  required arguments:
    --alice               alice
  </code></pre>
  
  <p>Is there any solution to list them as required? As <code>add_mutually_exclusive_group()</code> does not support the <code>title</code> parameter, I cannot do something like <code>add_mutually_exclusive_group('must pick one', required=True)</code></p>