Added `entrypoint.sh`

This wrapping scripts let me do debugging and more advanced features.

alpha

This is the earliest usable release I can come up with. You'll need to have pushed an image to docker hub and authenticated with a Kubernetes context that rio will be able to use with kubectl to access the Kubernetes cluster you're managing. See an example of doing this with Digital Ocean at:

https://github.com/andrewsomething/example-doctl-action/blob/master/.github/workflows/workflow.yaml