Add a section 'Extensions' (#246)

* Add a section 'Extensions'

* Update with the recommendations of Nick Coghlan

Author: matrixise

extensions.rst

@@ -0,0 +1,15 @@
+.. _extensions:
+
+Updating standard library extension modules
+===========================================
+
+In this section, we could explain how to write a CPython extension with the C language, but the topic can take a complete book.
+
+For this reason, we prefer to give you some links where you can read a very good documentation.
+
+Read the following references:
+
+* https://docs.python.org/dev/c-api/
+* https://docs.python.org/dev/extending/
+* https://www.python.org/dev/peps/pep-0399/
+* https://pythonextensionpatterns.readthedocs.io/en/latest/

index.rst

@@ -348,6 +348,7 @@ Full Table of Contents
    exploring
    grammar
    compiler
+   extensions
    coverity
    clang
    buildworker