docs: Initial README.md

Signed-off-by: Víctor Cuadrado Juan <vcuadradojuan@suse.de>

README

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+# Rego policies library
+
+This repository contains a collection of Rego policies that can be used with
+Kubewarden to enforce security and compliance best practices.
+
+These policies have been adapted from https://github.com/weaveworks/policy-library.
+Weaveworks has been a pioneer in the field of Kubernetes security and compliance and
+transitioned to a community-driven project with the closure of their company.
+We thank Weaveworks and their contributors for their work on these policies.
+
+The policies are organized as:
+- `policies/`: Production ready, tested policies, released via tags to
+  `ghcr.io/kubewarden/policies` and artifacthub.io.
+- `staging/`: Policies under evaluation, not yet released.
+
+## Releasing a policy
+
+Push a new tag with the pattern `PolicyName/vX.Y.Z`. The release job will test,
+build and push the policy to `ghcr.io/kubewarden/policies`, create the
+corresponding GH release, as well as updating the `artifacthub` branch in this
+repository.