title: argparse like docker cli
body: <p>Hello i am writing cmd tool,
  i want to have behaviour like docker does:</p>
  
  <p><code>docker container run --help</code></p>
  
  <p>print the help for this particular command.
  im stucked with code:</p>
  
  <p><code>parser.add_argument("method", help=getHelp())</code></p>
  
  <p>but the method can be anything like </p>
  
  <ul>
  <li>add</li>
  <li>remove</li>
  <li>update</li>
  </ul>
  
  <p>and how to later add a method in add like:</p>
  
  <ul>
  <li>add ram</li>
  <li>add cpu</li>
  </ul>
  
  <p>i can add subparser for add but how to add later a subparser for ram ?
  How can i achieve that with argparse in python?</p>
  
  <p>Is it even possible?</p>
  
  <p>Can somebody show me example of third deep command with its own arguments ?</p>