docs: supported version range

To be moved to the "production ready" tier in upstream's documentation,
we need to include the versions of Kubernetes and cert-manager
supported, and link to upstream's installation docs.

README.org

@@ -3,7 +3,12 @@
 Origin CA Issuer is a [[https://github.com/cert-manager/cert-manager][cert-manager]] CertificateRequest controller for Cloudflare's [[https://developers.cloudflare.com/ssl/origin-configuration/origin-ca][Origin CA]] feature.
 
 ** Getting Started
-We assume you have a Kubernetes cluster (1.16 or newer) with cert-manager (1.0 or newer) installed. We also assume you have permissions to create Custom Resource Definitions.
+*** Prerequisites
+
+- Kubernetes: releases with [[https://endoflife.date/kubernetes][maintenance support]]
+- cert-manager: releases under [[https://endoflife.date/cert-manager][upstream support]], which can be installed following upstream's [[https://cert-manager.io/docs/installation/][documentation]].
+
+You must also have permissions in the Kubernetes cluster to create Custom Resource Definitions.
 
 *** Installing Origin CA Issuer
 First, we need to install the Custom Resource Definitions for the Origin CA Issuer.

deploy/charts/origin-ca-issuer/Chart.yaml

@@ -1,7 +1,7 @@
 apiVersion: v2
 type: application
 name: origin-ca-issuer
-version: 0.5.7
+version: 0.5.8
 appVersion: 0.9.0
 description: A Helm chart for origin-ca-issuer
 home: https://github.com/cloudflare/origin-ca-issuer

deploy/charts/origin-ca-issuer/README.md

@@ -4,8 +4,8 @@ origin-ca-issuer is a Kubernetes addon to automate issuance and renewals of Clou
 
 ## Prerequisites
 
-* Kubernetes 1.16+
-* cert-manager 1.0.0+
+* Kubernetes releases in [maintenance support](https://endoflife.date/kubernetes)
+* cert-manager releases with upstream [support](https://endoflife.date/cert-manager)
 
 ## Installing the Chart