Drop Python 2.6 with 16.04.

xref galaxyproject#1596

doc/source/releases/16.01_announce.rst

@@ -65,6 +65,13 @@ Upgrade
 
 See `our wiki <https://wiki.galaxyproject.org/Develop/SourceCode>`__ for additional details regarding the source code locations.
 
+Deprecation Notices
+===========================================================
+
+Barring a strong outcry from deployers, 16.01 will be the last release of Galaxy to
+support Python 2.6. For more information, see Galaxy Github
+`Issue #1596 <https://github.com/galaxyproject/galaxy/issues/1596>`_.
+
 .. _eggs: https://pythonhosted.org/setuptools/formats.html
 .. _wheels: http://pythonwheels.com/
 .. _pip: https://pip.pypa.io/en/stable/