Fix crontab in README

README.md

@@ -36,11 +36,11 @@ grant all privileges on fiouldb.* TO 'fioul'@'localhost';
 Tables can be created by running `./fioul.py initdb`
 
 
-To update the database every 15 minutes, the following line can be
-installed as a cronjob:
+To update the database day at 9:30am, the following line can be installed as a
+cronjob:
 
 ```
-*/15 * * * * /opt/fioul/fioul.py update
+30 09 * * * /opt/fioul/fioul.py update
 ```
 
 To launch the server automatically, you can install and use the systemd