Refs #30944 -- Added pyproject.toml in reusable apps docs.

Related to f8f35e8.

docs/intro/reusable-apps.txt

@@ -183,12 +183,20 @@ this. For a small app like polls, this process isn't too difficult.
    license. Just be aware that your licensing choice will affect who is able
    to use your code.
 
-#. Next we'll create ``setup.cfg`` and ``setup.py`` files which detail how to
-   build and install the app. A full explanation of these files is beyond the
-   scope of this tutorial, but the `setuptools documentation
-   <https://setuptools.readthedocs.io/en/latest/>`_ has a good explanation.
-   Create the files ``django-polls/setup.cfg`` and ``django-polls/setup.py``
-   with the following contents:
+#. Next we'll create ``pyproject.toml``, ``setup.cfg``, and ``setup.py`` files
+   which detail how to build and install the app. A full explanation of these
+   files is beyond the scope of this tutorial, but the `setuptools
+   documentation <https://setuptools.readthedocs.io/en/latest/>`_ has a good
+   explanation. Create the ``django-polls/pyproject.toml``,
+   ``django-polls/setup.cfg``, and ``django-polls/setup.py`` files with the
+   following contents:
+
+   .. code-block:: toml
+        :caption: django-polls/pyproject.toml
+
+        [build-system]
+        requires = ['setuptools>=40.8.0', 'wheel']
+        build-backend = 'setuptools.build_meta:__legacy__'
 
    .. code-block:: ini
         :caption: django-polls/setup.cfg