doc: configuration

docs/config.rst

@@ -8,7 +8,18 @@ Installing and Configuring the Service
 ConfServ and Configuration File
 -------------------------------
 
-There is an optional configuration file::
+The service can be configured using a configuration file that is looked for in the following places:
+
+* ``/WEB-INF/aggregator.properties`` (i.e. built into the service)
+* ``file:${user.home}/.aggregator.properties``
+* ``file:/etc/textgrid/aggregator/aggregator.properties``
+
+The last one wins. The configuration file is basically simply used to set up
+the ConfServ endpoint from which the actual service endpoints are read. You can
+also use it to override ConfServ values, e.g., if you would like to bypass
+a proxy server.
+
+Here is the default configuration file::
 
   # The final endpoint that should be displayed in the generated WADL
   aggregator.endpoint.published=https://textgridlab.org/1.0/aggregator