Add instructions for cron(ie) setup

DOCS/installation.md

@@ -139,7 +139,7 @@ Use `php.ini` as additional PHP configuration (e.g. in `/etc/php/conf.d/servnest
 
 Use `php-fpm.conf` as the PHP-FPM configuration (e.g. in `/etc/php/php-fpm.d/servnest.conf`).
 
-### For systemd
+##### For systemd
 
 `php-fpm.service.override.conf` may be required as the PHP-FPM service configuration override.
 
@@ -298,3 +298,7 @@ Copy the configuration template to the actual configuration file and adapt it ac
 cp /srv/servnest/core/config.template.ini /srv/servnest/core/config.ini
 vim /srv/servnest/core/config.ini
 ```
+
+### Cronie
+
+Set the `cronie` file as `/etc/cron.d/servnest`.

README.md

@@ -68,6 +68,9 @@ Tor
 [Certbot](https://certbot.eff.org/)
 : get [Let's Encrypt](https://letsencrypt.org/) certificates for TLS
 
+Cronie (or another cron daemon)
+: periodically run script to sync registry records with child zones and pseudo-CNAMEs at apex
+
 [GNU Core Utilities](https://www.gnu.org/software/coreutils/) or [BusyBox](https://www.busybox.net/)
 : manipulate the filesystem through sudo