title: argparse add example usage
body: <p>I use argparse to deal with input parameters, and it outputs the following with parser.print_help():</p>
  
  <pre><code>optional arguments:
    -h, --help            show this help message and exit
    -t TEMPLATES, --templates TEMPLATES
                      template names to make, should be defined as section
                      name in conf, and have related file in templates/
                      folder
    -c CONFPATH, --confpath CONFPATH
                      configuration path for template detail info
  </code></pre>
  
  <p>my code looks like the following:</p>
  
  <pre><code>    import argparse
      parser = argparse.ArgumentParser(prog='base_maker', description='template maker')
      parser.add_argument('-t', '--templates', help='template names to make, should be defined as section name in conf, and have related file in templates/ folder', type=str)
      parser.add_argument('-c', '--confpath', help='configuration path for template detail info', type=str, default=os.path.join(basepath, 'conf/maker.conf'))
  </code></pre>
  
  <p>However, I want to add a detailed example about how to use -t/--template, like (added in the <strong>example</strong> part):</p>
  
  <pre><code>optional arguments:
    -h, --help            show this help message and exit
    -t TEMPLATES, --templates TEMPLATES
                      template names to make, should be defined as section
                      name in conf, and have related file in templates/
                      folder
    -c CONFPATH, --confpath CONFPATH
                      configuration path for template detail info
  
   example:
  
       python test.py -t template/test.py
       python test.py -t template/test -c conf/test.conf
       python test.py -t test.py
  </code></pre>
  
  <p>I don't know which attribute should be used to add "example" part, I check <a href="https://stackoverflow.com/questions/10930635/print-program-usage-example-with-argparse-module">Print program usage example with argparse modulen</a>, but it's unclear and without detailed example when I check <a href="https://docs.python.org/3/library/argparse.html#epilog" rel="noreferrer">epilog in the official doc</a>.</p>
  
  <p>Could anyone give me a example about how to achieve that? Thanks</p>