Correct an example in docs/modelforms.txt, and fix some reST formatting

    # Create a form instance with POST data.

    >>> a = Author()

    >>> f = AuthorForm(a, request.POST)

    >>> f = AuthorForm(request.POST, instance=a)

    # Create and save the new author instance. There's no need to do anything else.

    >>> new_author = f.save()

   created from the model via ``ModelForm`` will not include that

   field.

    2. Use the ``fields`` attribute of the ``ModelForm``'s inner ``Meta`` class.

       This attribute, if given, should be a list of field names to include in

       the form.

2. Use the ``fields`` attribute of the ``ModelForm``'s inner ``Meta``

   class.  This attribute, if given, should be a list of field names

   to include in the form.

    3. Use the ``exclude`` attribute of the ``ModelForm``'s inner ``Meta`` class.

       This attribute, if given, should be a list of field names to exclude

       the form.

3. Use the ``exclude`` attribute of the ``ModelForm``'s inner ``Meta``

   class.  This attribute, if given, should be a list of field names

   to exclude the form.

       For example, if you want a form for the ``Author`` model (defined above)

       that includes only the ``name`` and ``title`` fields, you would specify

       ``fields`` or  ``exclude`` like this::

For example, if you want a form for the ``Author`` model (defined

above) that includes only the ``name`` and ``title`` fields, you would

specify ``fields`` or ``exclude`` like this::

    class PartialAuthorForm(ModelForm):

        class Meta: