DOC: warn about pending deprecation of data pkgs

The data packages described in data_pkg_discuss are going to go away
fairly soon, and no-one should be starting a new package using this
system.

Author: matthew-brett

doc/source/devel/data_pkg_discuss.rst

@@ -4,6 +4,17 @@
 Principles of data package
 ##########################
 
+*******
+Summary
+*******
+
+This is a discussion of data packages, as they are currently implemented in
+nibabel / nipy.
+
+This API proved to be very uncomfortable, and we intend to replace it fairly
+soon.  See ``data_packages.rst`` in the `nibabel wiki`_ for our current
+thinking, not yet implemented.
+
 **********
 Motivation
 **********

doc/source/links_names.txt

@@ -19,6 +19,7 @@
 .. _nibabel pypi: http://pypi.python.org/pypi/nibabel
 .. _nibabel issues: http://github.com/nipy/nibabel/issues
 .. _nibabel github issues: http://github.com/nipy/nibabel/issues
+.. _nibabel wiki: https://github.com/nipy/nibabel.wiki
 
 .. other related projects
 .. _nipy community: http://nipy.org