Fixed #24672 -- Clarified note about installing postgis_topology

    $ createdb  <db name>

    $ psql <db name>

    > CREATE EXTENSION postgis;

    > CREATE EXTENSION postgis_topology;

No PostGIS topology functionalities are yet available from GeoDjango, so the

creation of the ``postgis_topology`` extension is entirely optional.

GeoDjango does not currently leverage any `PostGIS topology functionality`__.

If you plan to use those features at some point, you can also install the

``postgis_topology`` extension by issuing ``CREATE EXTENSION

postgis_topology;``.

__ http://postgis.net/docs/Topology.html

.. versionchanged:: 1.8