limit journalctl usage

```
$ realpath limits.conf 
/etc/systemd/journald.conf.d/limits.conf

$ cat limits.conf 
[Journal]
SystemMaxUse=500M
SystemKeepFree=100M
SystemMaxFileSize=100M
RuntimeMaxUse=100M
RuntimeKeepFree=100M
RuntimeMaxFileSize=200M
```

`sudo systemctl restart systemd-journald`