Document how to backport

docs/source/coredev/index.rst

@@ -1,29 +1,56 b''
 .. _core_developer_guide:
 
 =================================
 Guide for IPython core Developers
 =================================
 
 This guide documents the development of IPython itself.  Alternatively,
 developers of third party tools and libraries that use IPython should see the
 :doc:`../development/index`.
 
 
 For instruction on how to make a developer install see :ref:`devinstall`.
 
 .. toctree::
    :maxdepth: 1
 
    release_process
 
 
+Backporting Pull requests
+-------------------------
+
+All pull requests should usually be made against ``master``, if a Pull Request
+need to be backported to an earlier release; then it should be tagged with the
+correct ``milestone``. We then use `ghpro <https://pypi.python.org/pypi/ghpro>`
+to automatically list and apply the PR on other branches. For example:
+
+.. code-block:: bash
+    
+    $ backport-pr todo --milestone 5.2
+    [...snip..]
+    The following PRs have been backported
+    9848
+    9851
+    9953
+    9955
+    The following PRs should be backported:
+    9417
+    9863
+    9925
+    9947
+
+    $ backport-pr apply 5.x 9947
+    [...snip...]
+
+
 Old Documentation
 =================
 
 Out of date documentation is still available and have been kept for archival purposes.
 
 .. note::
 
   Developers documentation used to be on the IPython wiki, but are now out of
   date. The wiki is though still available for historical reasons: `Old IPython
   GitHub Wiki.  <https://github.com/ipython/ipython/wiki/Dev:-Index>`_