[1.9.x] Added docs example for manually creating a column with RunSQL.

manually creating a column, you should pass in a list containing an ``AddField``

operation here so that the autodetector still has an up-to-date state of the

model (otherwise, when you next run ``makemigrations``, it won't see any

operation that adds that field and so will try to run it again).

operation that adds that field and so will try to run it again). For example::

    migrations.RunSQL(

        "ALTER TABLE musician ADD COLUMN name varchar(255) NOT NULL;",

        state_operations=[

            migrations.AddField(

                'musician',

                'name',

                models.CharField(max_length=255),

            ),

        ],

    )

The optional ``hints`` argument will be passed as ``**hints`` to the

:meth:`allow_migrate` method of database routers to assist them in making