Warn when rules.yml are not found

[Rodeoclash]

I have a reasonably complicated setup where my rules.yml file is templated in Terraform then downloaded to the container using a sidecar. Or, it would be had I remembered to configure the sidecar to actually download the file.

Perhaps we should log a warning if a rules.yml is specified but not found.

[vinckr]

Hey Samuel,
this sounds like a reasonable addition to me.
Feel free to create a design document or pull request if you are willing to work on this.