Swift: add QLdoc for Generated modules

Author: redsun82

misc/codegen/templates/ql_class.mustache

@@ -10,6 +10,10 @@ private import {{import_prefix}}.Raw
 import {{.}}
 {{/imports}}
 
+/**
+ * INTERNAL: This module contains the fully generated definition of `{{name}}` and should not
+ * be referenced directly.
+ */
 module Generated {
   /**
   {{#doc}}