Minor precision in template_list doc, to always use a custom list_id when using default UI_UL_list class.

source/blender/makesrna/intern/rna_ui_api.c

@@ -771,7 +771,8 @@ void RNA_api_ui_layout(StructRNA *srna)
 	parm = RNA_def_string(func, "listtype_name", "", 0, "", "Identifier of the list type to use");
 	RNA_def_property_flag(parm, PROP_REQUIRED);
 	parm = RNA_def_string(func, "list_id", "", 0, "",
-	                      "Identifier of this list widget. "
+	                      "Identifier of this list widget (should be systematically used with default UI_UL_list "
+	                      "class). "
 	                      "If this is set, the uilist gets a custom ID, otherwise it takes the "
 	                      "name of the class used to define the uilist (for example, if the "
 	                      "class name is \"OBJECT_UL_vgroups\", and list_id is not set by the "