added an example with array in the docs

modules/core/docs/authproc_attributecopy.md

 `core:AttributeCopy`
 ===================
 
-Filter that renames attributes.
+Filter that copies attributes.
 
 
 Examples
 --------
 
-Copy a single attribute (user's uid will be copied to the user's username):
+Copy a single attribute (user's `uid` will be copied to the user's `username`):
 
     'authproc' => array(
         50 => array(
@@ -16,3 +16,11 @@ Copy a single attribute (user's uid will be copied to the user's username):
         ),
     ),
 
+Copy a single attribute to more then one attribute (user's `uid` will be copied to the user's `username` and to `urn:mace:dir:attribute-def:uid`)
+
+    'authproc' => array(
+        50 => array(
+            'class' => 'core:AttributeCopy',
+            'uid' => array('username', 'urn:mace:dir:attribute-def:uid'),
+        ),
+    ),