Added config reference for router.default_uri

Author: Nyholm

reference/configuration/framework.rst

@@ -190,6 +190,7 @@ Configuration
 
 * `router`_
 
+  * `default_uri`_
   * `http_port`_
   * `https_port`_
   * `resource`_
@@ -1145,6 +1146,14 @@ The type of the resource to hint the loaders about the format. This isn't
 needed when you use the default routers with the expected file extensions
 (``.xml``, ``.yaml``, ``.php``).
 
+default_uri
+.........
+
+**type**: ``string``
+
+The default URI used to generate URLs in a non-HTTP context  (see
+:doc:`/routing`#generating-urls-in-commands).
+
 http_port
 .........