Fixed #22482 -- Recommended using data migrations in contrib.sites docs.

:data:`~django.db.models.signals.post_migrate` signal handler which creates a

default site named ``example.com`` with the domain ``example.com``. This site

will also be created after Django creates the test database. To set the

correct name and domain for your project, you can use an :doc:`initial data

fixture </howto/initial-data>`.

correct name and domain for your project, you can use a :ref:`data migration

<data-migrations>`.

Caching the current ``Site`` object

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