title: Show message only when using --help in python click
body: <p>I am contributing to open source project which uses click for it's command line interface.</p>
  <p>I want to show a message <strong>only</strong> when the <code>--help</code> flag is used</p>
  <p><strong>Expected Result</strong></p>
  <p><code> manim --help</code></p>
  <pre><code>normal cli stuff that was there before
  
  
  The message I'd like to add
  </code></pre>
  <p><strong>What I've tried</strong></p>
  <ol>
  <li>Using @click.option</li>
  </ol>
  <pre><code>@click.option(
      &quot;--help&quot;,
      is_flag=True,
      help=&quot;For more information regarding configuration and rendering&quot;
  )
  </code></pre>
  <p>Output:</p>
  <pre><code>Manim Community v0.9.0
  
  Usage: manim [OPTIONS] COMMAND [ARGS]...
  
  Error: Missing command.
  </code></pre>
  <p>NOTE: This is the file that I'm trying to change if it's helpful</p>
  <p><a href="https://github.com/ManimCommunity/manim/blob/main/manim/__main__.py" rel="nofollow noreferrer">https://github.com/ManimCommunity/manim/blob/main/manim/__main__.py</a></p>