--- plugins/calendar/config.inc.php.dist.orig	2021-02-18 09:45:46 UTC
+++ plugins/calendar/config.inc.php.dist
@@ -25,6 +25,13 @@
  +-------------------------------------------------------------------------+
 */
 
+/*
+ * In order to initialise the calendar database tables, on first setup it
+ * is necessary to run (for example, if you are using MySQL):
+ *
+ * # mysql roundcubemail < %%WWWDIR%%/calendar/drivers/database/SQL/mysql.initial.sql
+ */
+
 // backend type (database, kolab)
 $config['calendar_driver'] = "database";