README: document submodule usage

This tells people who didn't read the commit message what to do with
the changes from:

  commit 8e10f59d36ea9c619241efaf3213156406dd74f9
  Author: W. Trevor King <wking@tremily.us>
  Date:   Tue Dec 11 11:30:24 2012 -0500

    dep: add pygrader dependencies as submodules

diff --git a/README b/README
index 14ee7645f1dd9b7d0e8ea5e3fc326a73c98e710f..52ca617248fea0d15a23dfa9b121097baa7eb16b 100644 (file)
--- a/README
+++ b/README
@@ -55,6 +55,36 @@ standard::
 
   $ python setup.py install
 
+Submodules
+----------
+
+pgp-mime_ depends on pyassuan_, which requires Python 3.3.  If your
+distribution doesn't package Jinja_ or ``pgp-mime`` for Python 3.3,
+you can use ``pygrader``'s Git submodules to easily fetch compatible
+versions.  The submodules are stored in the ``dep/src`` directory with
+symbolic links in ``dep`` itself.  For example, the ``pgp-mime``
+submodule is kept in ``dep/src/pgp-mime`` with the symlink
+``dep/pgp_mime`` pointing to ``dep/pgp-mime/pgp_mime``.  If you only
+need a few submodules, you can initialize them explicitly::
+
+  $ git submodule init pgp-mime pyassuan
+
+If you want all of the submodules, use::
+
+  $ git submodule init
+
+Git submodule will fetch (when necessary) and unpack the gitlinked
+commit of initialized submodules with::
+
+  $ git submodule update
+
+You'll want to run ``update`` again after any superproject (in this
+case, ``pygrader``) action that updates the gitlinks.  Once you have
+checked out the dependencies you need, point ``PYTHONPATH`` to the
+``dep`` directory whenever you run ``pygrader``.  For example::
+
+  $ PYTHONPATH=dep ./bin/pg.py ...
+
 Usage
 =====
 
@@ -324,6 +354,7 @@ using graphical interfaces.
 .. _Gentoo: http://www.gentoo.org/
 .. _Jinja: http://jinja.pocoo.org/
 .. _pgp-mime: http://blog.tremily.us/posts/pgp-mime/
+.. _pyassuan: http://blog.tremily.us/posts/pyassuan/
 .. _NumPy: http://numpy.scipy.org/
 .. _update-copyright: http://blog.tremily.us/posts/update-copyright/
 .. _Git: http://git-scm.com/