Merge pull request realpython#337 from phalt/add_python_packaging_guide_link

Added link to the python packaging guide.

Author: kennethreitz

docs/shipping/packaging.rst

@@ -5,6 +5,8 @@ Packaging your code is important.
 
 You'll need to package your code first before sharing it with other developers.
 
+The `Python Packaging Guide <https://python-packaging-user-guide.readthedocs.org/en/latest/>`_ provides an extensive guide on creating and maintaining Python packages.
+
 For Python Developers
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