Add documentation for category_tree template tag.
Template tags
=============
+Category tags
+-------------
+
+Load these tags using ``{% load category_tags %}``.
+
+``category_tree``
+~~~~~~~~~~~~~~~~~
+
+Generates an annotated list of categories in a structure indented for easy
+rendering of a nested tree in a single loop:
+
+.. code-block:: html+django
+
+ {% category_tree as tree_categories %}
+ <ul>
+ {% for category, info in tree_categories %}
+ <li>
+ <a href="{{ category.get_absolute_url }}">{{ category.name }}</a>
+ {% if info.has_children %}
+ <ul>
+ {% else %}
+ </li>
+ {% endif %}
+ {% for n in info.num_to_close %}
+ </ul></li>
+ {% endfor %}
+ {% endfor %}
+ </ul>
+
+Each item in the list is a tuple of the form:
+
+.. code-block:: python
+
+ (
+ category,
+ {
+ 'has_children': True, # Whether this node has children in the tree
+ 'level': 1, # The depth of this node
+ 'num_to_close', # A list indicating the number of leaf branches that
+ # this category terminates.
+ }
+ )
+
+The arguments are:
+
+=================== =====================================================
+Argument Description
+=================== =====================================================
+``depth`` The depth to which to fetch child categories
+``parent`` The parent category for which to get a list of children
+=================== =====================================================
+
Shipping tags
-------------
