Fixed #846 -- Fixed bug in docs/syndication_feeds.txt. Thanks, deric

This example illustrates all possible attributes and methods for a ``Feed`` class::

    class ExampleFeed(rss.Feed):

    from django.contrib.syndication.feeds import Feed

    from django.utils import feedgenerator

    class ExampleFeed(Feed):

        # FEED TYPE -- Optional. This should be a class that subclasses

        # django.utils.feedgenerator.SyndicationFeed. This designates which