[IMP] developer/howtos/rdtraining: Add missing information about module category.

Adds explanations and directive for module category creation, so it can be used correctly at res.groups creation.

closes odoo/documentation#2721

Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>

content/developer/howtos/rdtraining/B_acl_irrules.rst

@@ -88,27 +88,27 @@ the ``res.groups`` model. They are normally part of a module's :ref:`master data
 
 As simple example `can be found here <https://github.com/odoo/odoo/blob/532c083cbbe0ee6e7a940e2bdc9c677bd56b62fa/addons/hr/security/hr_security.xml#L9-L14>`_.
 
-.. admonition:: what is the *category_id*?
-
-    ``category_id`` a *module category*, it is automatically generated from the
-    :ref:`category defined in module manifest files <howto/rdtraining/03_newapp>`.
-
-    .. todo:: the demo module needs to have the category set, to
-              *Real Estate/Brokerage*, ideally the newapp part would already do
-              that
-
 .. exercise::
 
-    Create the ``security.xml`` file in the appropriate folder and add it to the
-    ``__manifest__.py`` file.
+    #. Create the ``security.xml`` file in the appropriate folder and add it to the ``__manifest__.py`` file.
 
-    Add a record creating a group with the id ``estate_group_user``, the name
-    "Agent" and the category ``base.module_category_real_estate_brokerage``.
+    #. If not already, add a ``'category'`` field to your ``__manifest__.py`` with value ``Real Estate/Brokerage``.
 
-    Below that, add a record creating a group with the id
-    ``estate_group_manager``, the name "Manager" and the category
-    ``base.module_category_real_estate_brokerage``. The ``estate_group_manager``
-    group needs to imply ``estate_group_user``.
+    #. Add a record creating a group with the id ``estate_group_user``, the name "Agent"
+       and the category ``base.module_category_real_estate_brokerage``.
+
+    #. Below that, add a record creating a group with the id ``estate_group_manager``,
+       the name "Manager" and the category ``base.module_category_real_estate_brokerage``.
+       The ``estate_group_manager`` group needs to imply ``estate_group_user``.
+
+    .. note::
+
+        Where does that **category** comes from ? It's a *module category*.
+        Here we used the category id ``base.module_category_real_estate_brokerage``
+        which was automatically generated by Odoo based on the `category` set in the ``__manifest__.py`` of the module.
+        You can also find here the list of
+        `default module categories <https://github.com/odoo/odoo/blob/71da80deb044852a2af6b111d695f94aad7803ac/odoo/addons/base/data/ir_module_category_data.xml>`_
+        provided by Odoo.
 
     .. tip::