Updated timezone docs to use timezone.now()

    now = datetime.datetime.now()

When time zone support is enabled, Django uses time-zone-aware datetime

objects. If your code creates datetime objects, they should be aware too. In

this mode, the example above becomes::

When time zone support is enabled (:setting:`USE_TZ=True <USE_TZ>`), Django uses

time-zone-aware datetime objects. If your code creates datetime objects, they

should be aware too. In this mode, the example above becomes::

    import datetime

    from django.utils.timezone import utc

    now = datetime.datetime.utcnow().replace(tzinfo=utc)

.. note::

    from django.utils import timezone

    :mod:`django.utils.timezone` provides a

    :func:`~django.utils.timezone.now()` function that returns a naive or

    aware datetime object according to the value of :setting:`USE_TZ`.

    now = timezone.now()

.. warning::

       >>> import datetime

       >>> from django.utils import timezone

       >>> naive = datetime.datetime.utcnow()

       >>> aware = naive.replace(tzinfo=timezone.utc)

       >>> aware = timezone.now()

       >>> naive == aware

       Traceback (most recent call last):

       ...