Fixed #10559 -- Clarified documentation on customization of comments pages....

In the ``models.py`` we'll define a ``CommentWithTitle`` model::

    from django.db import models

    from django.contrib.comments.models import BaseCommentAbstractModel

    from django.contrib.comments.models import Comment

    class CommentWithTitle(BaseCommentAbstractModel):

    class CommentWithTitle(Comment):

        title = models.CharField(max_length=300)

All custom comment models must subclass :class:`BaseCommentAbstractModel`.

Most custom comment models will subclass the :class:`Comment` model. However,

if you want to substantially remove or change the fields available in the

:class:`Comment` model, but don't want to rewrite the templates, you could

try subclassing from :class:`BaseCommentAbstractModel`.

Next, we'll define a custom comment form in ``forms.py``. This is a little more

tricky: we have to both create a form and override