minor tweaks to PICCOLO_CONF docs

Author: dantownsend

docs/src/piccolo/engines/index.rst

@@ -95,9 +95,11 @@ variable accordingly.
 
     DB = SQLiteEngine(path='my_test_db.sqlite')
 
-If the ``picolo_conf`` file is located in a sub-module (rather than the root of your project) you can specify the path:
+If the ``piccolo_conf.py`` file is located in a sub-module (rather than the
+root of your project) you can specify the path like this:
 
 .. code-block:: bash
+
     export PICCOLO_CONF=sub_module.piccolo_conf
 
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