doc: update README with cronjob instructions

- add section about recommended crontab usage
- provide example of how to set up cron job for dc-ops
- remind users to set up logrotate for the log file

🤖

README.md

@@ -18,6 +18,14 @@ See `requirements.txt`
 2. Adapt `config.yml.example` to your needs and save it as `config.yml`
 3. Run `dc-ops` from the shell or from a cron job
 
+### Cron
+
+Recommended crontab usage:
+
+`*/15 * * * * python3 /opt/dc-ops/dc-ops 2>&1 | ts "\%FT\%H:\%M:\%S" >>/var/log/dc-ops.log`
+
+(do not forget logrotate)
+
 ## Parameters
 
 See `dc-ops --help`