Use 'options.entry_points' (setup.cfg) in docs

Let's document the best practices :)

docs/extensions.rst

@@ -349,6 +349,7 @@ implementation of the :ref:`namespace extension <examples/namespace-extension>`
 as well as the `pyproject extension`_ which serves as a blueprint for new
 extensions.
 
+
 Activating Extensions
 ---------------------
 
@@ -359,14 +360,13 @@ This is possible by setting up a `setuptools entry point`_ under the
 This entry point should point to our extension class, e.g. ``AwesomeFiles``
 like defined above. If you for instance use a scaffold generated by PyScaffold
 to write a PyScaffold extension (we hope you do ;-), you would add the following
-to the ``entry_points`` variable in ``setup.py``:
+to the ``options.entry_points`` section in ``setup.cfg``:
 
-.. code-block:: python
+.. code-block:: ini
 
-    entry_points = """
-    [pyscaffold.cli]
-    awesome_files = your_package.your_module:AwesomeFiles
-    """
+    [options.entry_points]
+    pyscaffold.cli =
+        awesome_files = your_package.your_module:AwesomeFiles
 
 
 Examples
@@ -402,15 +402,18 @@ development can be easily bootstrapped with the command::
 
     putup pyscaffoldext-${EXT_NAME} -p ${EXT_NAME} --namespace pyscaffoldext --no-skeleton
 
-If you put your extension code in the module ``extension.py`` then the ``entry_points``
-variable in ``setup.py`` looks like:
+If you put your extension code in the module ``extension.py`` then the
+``options.entry_points`` section in ``setup.cfg`` looks like:
 
-.. code-block:: python
+.. code-block:: ini
 
-    entry_points = """
-    [pyscaffold.cli]
-    awesome_files = pyscaffoldext.${EXT_NAME}.extension:AwesomeFiles
-    """
+    [options.entry_points]
+    pyscaffold.cli =
+        awesome_files = pyscaffoldext.${EXT_NAME}.extension:AwesomeFiles
+
+In this example, ``AwesomeFiles`` represents the name of the class that
+implementes the extension and ``awesome_files`` is the string used to create
+the flag for the ``putup`` command (``--awesome-files``).
 
 
 Final Considerations