update readme

Author: chrisns

README.md

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+# Policy checker
+
+This is a tool that can be used locally and in CI by tooling to determine if the repository is compliant with policy.
+
+The version of policy is determined by:
+ - Kubernetes: reads the `kustomization.yaml` file and retrieves the `commonLabels['mycompany.com/policy-version']`
+ - Terraform: reads the variable default_value of `mycompany.com/policy-version`
+
+If theres any `.tf` files it'll check terraform and check kubernetes if theres a `kustomization.yaml`.
+asdasdaff
+
+## ⚠️⚠️ This is not intended for general use or to be immediately reusable ⚠️⚠️
+The location of the policy it retrieves is hardcoded to get from [example-policy-org/policy](https://github.com/example-policy-org/policy). This was a very concious limitation to scope this to the proof of concept of the [example-policy-org github org](https://github.com/example-policy-org), to make this more reusable it needs to handle authenticating to retrieve the policy where it's in a private repo, be a significantly smaller image, cache the policy so it doesn't need to be retrieved on every execution and find a better story than docker to be able to execute locally for the sake of speed.
+
+## Usage
+
+```bash
+$ docker run --rm -v $(pwd):/apps ghcr.io/example-policy-org/policy-checker
+```