Provide example of cache setting.

Author: austin-hilberg

docs-parts/admin/5-blob-config_lang3.rst

@@ -1 +1,5 @@
-   This is done using ``dj.config`` to change the ``cache`` property.
+  This is done by saving the path in the ``cache`` key of the DataJoint configuration dictionary:
+
+  .. code-block:: python
+
+    dj.config['cache'] = '/temp/dj-cache'