Fix #1052: add comments to tarantoolctl configuration

extra/dist/default/tarantool.in

--- Options for Tarantool
+--
+-- System-wide settings for tarantoolctl and init scripts
+--
+-- This file was configured by the package maintainers and you probably
+-- don't want to change it. Please complain about your custom configuration
+-- directly to upstream's bug tracker rather than to your distro.
+--
+-- Settings below should be kept in sync with:
+--
+--   * logrotate configuration
+--   * tarantool.service unit
+--   * systemd-tmpfiles configuration
+--   * directory structure and permissions
+--
+
 default_cfg = {
     pid_file   = "@TARANTOOL_RUNDIR@", -- @TARANTOOL_RUNDIR@/${INSTANCE}.pid
     wal_dir    = "@TARANTOOL_DATADIR@", -- @TARANTOOL_DATADIR@/${INSTANCE}/