Document how to bundle policies

[lcarva]

As a policy author, I want to bundle the policy rules I wrote. Just like it's done for the policy rules in this repository, e.g. quay.io/enterprise-contract/ec-release-policy:git-00fcc20@sha256:b8a070cb63fd2bdc73bba448e427be14cdb4887ec20a88369c33916a06249159.

I've used EC in the past and am somewhat comfortable with it. But I don't know anything about oras or conftest. I do know a little bit of rego.

Acceptance Criteria

• Document how to package policy rules in a bundle.