docs: adds entityless attribute to the config template

closes #153

config-templates/perun_attributes.php

@@ -252,4 +252,13 @@ $config = [
         'ldap' => 'capabilities',
         'type' => 'array',
     ],
+
+    /*
+     * ENTITYLESS ATTRIBUTES
+     */
+    'perunEntitylessAttribute_orgAups' => [
+        'rpc' => 'urn:perun:entityless:attribute-def:def:orgAups',
+        'ldap' => '',
+        'type' => 'dictionary',
+    ],
 ];