Docs: simple example does not work

[brycenesbitt]

Implementing 'A simple example' at
​https://docs.djangoproject.com/en/dev/ref/contrib/syndication/

Gives error
Give your Entry class a get_absolute_url() method, or define an item_link() method in your Feed class.

Due to a missing 'def item_link(self, item):'

[Aymeric Augustin]

The example doesn't include the definition of the model; I suppose it had a get_absolute_url method.

It will be more explicit to import reverse at the beginning of the example and add something like:

    def item_link(self, item):
        return reverse('news-item', args=[item.pk])

[Claude Paroz]

Also add a comment above the method telling that item_link is only needed if NewsItem has no get_absolute_url.

[Tim Graham <timograham@…>]

In 1f1f60d12f78ee68d59b577fdb6a31857b1d0f44:

Fixed #19306 - Improved syndication example.

Thanks brycenesbitt for the report.

[Tim Graham <timograham@…>]

In 17c61aaea303a5f21537d9978c28135f6f17b489:

[1.5.X] Fixed #19306 - Improved syndication example.

Thanks brycenesbitt for the report.

Backport of 1f1f60d12f from master