PEP 12: Extract Intersphinx section. Add example of Intersphinx reference. (#3827)

* PEP 12: Extract Intersphinx section. Add example of Intersphinx reference.

* Update peps/pep-0012.rst

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

---------

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

peps/pep-0012.rst

@@ -647,8 +647,27 @@ If you find that you need to use a backslash in your text, consider
 using inline literals or a literal block instead.
 
 
-Canonical Documentation and Intersphinx
----------------------------------------
+Intersphinx
+-----------
+
+You can use
+`Intersphinx references
+<https://www.sphinx-doc.org/en/master/usage/extensions/intersphinx.html>`_
+to other Sphinx sites,
+such as the `Python documentation <https://docs.python.org/>`_
+`packaging.python.org <https://packaging.python.org/>`_,
+and `typing.readthedocs.io <https://typing.readthedocs.io/>`_,
+to easily cross-reference pages, sections and Python/C objects.
+
+For example,
+to create a link pointing to a section of the typing docs,
+you would write the following::
+
+    :ref:`type expression <typing:type-expression>`
+
+
+Canonical Documentation
+-----------------------
 
 As :pep:`PEP 1 describes <1#pep-maintenance>`,
 PEPs are considered historical documents once marked Final,
@@ -659,15 +678,6 @@ or an appropriate subclass:
 * ``canonical-pypa-spec`` for packaging standards
 * ``canonical-typing-spec`` for typing standards
 
-Furthermore, you can use
-`Intersphinx references
-<https://www.sphinx-doc.org/en/master/usage/extensions/intersphinx.html>`_
-to other Sphinx sites,
-currently the `Python documentation <https://docs.python.org/>`_
-and `packaging.python.org <https://packaging.python.org/>`_,
-to easily cross-reference pages, sections and Python/C objects.
-This works with both the "canonical" directives and anywhere in your PEP.
-
 Add the directive between the headers and the first section of the PEP
 (typically the Abstract)
 and pass as an argument an Intersphinx reference of the canonical doc/spec