Raise an error if config file path does not exist?

Hi there 👋

Today I learned that if `-c` resp. `--config-file` option points to a path that doesn't exist, it falls back to a default config.

```sh
bin/jobs --config-file="config/this-file-does-not-exist.yml"
```

I wonder if it should rather raise an error if the file does not exist?
Or maybe a warning that it falls back to a default?