Add command to renew certbot certificates

Guides/httpd.md

@@ -11,3 +11,9 @@ Create a new configuration in `/etc/apache2/sites-available`
 Enable a configuration by creating a likn in `/etc/apache2/sites-enabled`
 
 `sudo ln --symbolic ../sites-available/kanboard.jovian-hersemeule.eu.conf kanboard.jovian-hersemeule.eu.conf`
+
+## Certbot
+
+To renew certificates :
+
+`sudo certbot --apache renew`