Documented INSTALLED_APPS requirement for HStoreField.

    A field for storing mappings of strings to strings. The Python data type

    used is a ``dict``.

    To use this field, you'll need to setup the hstore extension in PostgreSQL

    by adding a migration with the

    To use this field, you'll need to:

    1. Add ``'django.contrib.postgres'`` in your :setting:`INSTALLED_APPS`.

    2. Setup the hstore extension in PostgreSQL before the first ``CreateModel``

       or ``AddField`` operation by adding a migration with the

       :class:`~django.contrib.postgres.operations.HStoreExtension` operation.

    You'll see an error like ``'type "hstore" does not exist'`` if you skip

    this step.

    You'll see an error like ``can't adapt type 'dict'`` if you skip the first

    step, or ``type "hstore" does not exist`` if you skip the second.

.. note::