title: How to add to setup.cfg the extensions block
body: <p>In my Python project I have only <strong>setup.cfg</strong> and <strong>pyproject.toml</strong> configuration files and I don't want to add <strong>setup.py</strong>. But I want to use Sphinx package and it requires to add the extensions block to the <em>setup.py</em> (like <a href="https://stackoverflow.com/questions/13516404/sphinx-error-unknown-directive-type-automodule-or-autoclass">answered here</a>):</p>
  <pre><code>extensions = ['sphinx.ext.todo', 'sphinx.ext.viewcode', 'sphinx.ext.autodoc']
  </code></pre>
  <p>So how can I add this section to the <em>setup.cfg</em>?</p>