added documentation on Model attributes

A complete list of all possible ``Meta`` options can be found in the :doc:`model

option reference </ref/models/options>`.

.. _model-attributes:

Model attributes

================

:attr:`~objects`

    The most important attribute of a model is the 

    :class:`~django.db.models.Manager`, which is the interface through which 

    database query operations are provided to Django models and is used to 

    :ref:`retrieve the instances <retrieving-objects>` from the database. If no 

    custom Manager is defined, the default name is ``objects``. Managers are 

    only accessible via model classes, not the model instances. 

.. _model-methods:

Model methods

Django will complain if you try to assign or add an object of the wrong type.

.. _retrieving-objects:

Retrieving objects

==================