Describe using PyPI/pip to distribute & install extensions

From discussion on gh-5742

docs/source/config/extensions/index.rst

@@ -1,92 +1,100
 .. _extensions_overview:
 
 ==================
 IPython extensions
 ==================
 
 A level above configuration are IPython extensions, Python modules which modify
 the behaviour of the shell. They are referred to by an importable module name,
 and can be placed anywhere you'd normally import from, or in
 ``.ipython/extensions/``.
 
 Getting extensions
 ==================
 
 A few important extensions are :ref:`bundled with IPython <bundled_extensions>`.
 Others can be found on the `extensions index
-<https://github.com/ipython/ipython/wiki/Extensions-Index>`_ on the wiki, and installed with
-the ``%install_ext`` magic function.
+<https://github.com/ipython/ipython/wiki/Extensions-Index>`_ on the wiki, and
+the `Framework :: IPython tag <https://pypi.python.org/pypi?:action=browse&c=586>`_
+on PyPI.
+
+Extensions on PyPI can be installed using ``pip``, like any other Python package.
+Other simple extensions can be installed with the ``%install_ext`` magic. The
+latter does no validation, so be careful using it on untrusted networks like
+public wifi.
 
 Using extensions
 ================
 
 To load an extension while IPython is running, use the ``%load_ext`` magic:
 
 .. sourcecode:: ipython
 
     In [1]: %load_ext myextension
 
 To load it each time IPython starts, list it in your configuration file::
 
     c.InteractiveShellApp.extensions = [
         'myextension'
     ]
 
 Writing extensions
 ==================
 
 An IPython extension is an importable Python module that has a couple of special
 functions to load and unload it. Here is a template::
 
     # myextension.py
 
     def load_ipython_extension(ipython):
         # The `ipython` argument is the currently active `InteractiveShell`
         # instance, which can be used in any way. This allows you to register
         # new magics or aliases, for example.
 
     def unload_ipython_extension(ipython):
         # If you want your extension to be unloadable, put that logic here.
 
 This :func:`load_ipython_extension` function is called after your extension is
 imported, and the currently active :class:`~IPython.core.interactiveshell.InteractiveShell`
 instance is passed as the only argument. You can do anything you want with
 IPython at that point.
 
 :func:`load_ipython_extension` will be called again if you load or reload
 the extension again. It is up to the extension author to add code to manage
 that.
 
 Useful :class:`InteractiveShell` methods include :meth:`~IPython.core.interactiveshell.InteractiveShell.register_magic_function`, 
 :meth:`~IPython.core.interactiveshell.InteractiveShell.push` (to add variables to the user namespace) and 
 :meth:`~IPython.core.interactiveshell.InteractiveShell.drop_by_id` (to remove variables on unloading).
 
 .. seealso::
 
    :ref:`defining_magics`
 
 You can put your extension modules anywhere you want, as long as they can be
 imported by Python's standard import mechanism. However, to make it easy to
 write extensions, you can also put your extensions in :file:`extensions/`
 within the :ref:`IPython directory <ipythondir>`. This directory is
 added to :data:`sys.path` automatically.
 
 When your extension is ready for general use, please add it to the `extensions
-index <https://github.com/ipython/ipython/wiki/Extensions-Index>`_.
+index <https://github.com/ipython/ipython/wiki/Extensions-Index>`_. We also
+encourage you to upload it to PyPI and use the ``Framework :: IPython``
+classifier, so that users can install it with standard packaging tools.
 
 .. _bundled_extensions:
 
 Extensions bundled with IPython
 ===============================
 
 .. toctree::
    :maxdepth: 1
 
    autoreload
    cythonmagic
    rmagic
    storemagic
    sympyprinting
 
 * ``octavemagic`` used to be bundled, but is now part of `oct2py <http://blink1073.github.io/oct2py/docs/>`_.
   Use ``%load_ext oct2py.ipython`` to load it.