add postgres-cluster-upgrade chart

charts/postgres-cluster-upgrade/README.md

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+## Introduction
+
+[CloudNative PG](https://github.com/cloudnative-pg/cloudnative-pg)
+
+CloudNativePG is the Kubernetes operator that covers the full lifecycle of a highly available PostgreSQL database cluster with a primary/standby architecture, using native streaming replication.
+
+This chart bootstraps a [CNPG](https://github.com/cloudnative-pg/cloudnative-pg) cluster on a [Kubernetes](https://kubernetes.io) cluster using the [Helm](https://helm.sh) package manager.
+
+## Prerequisites
+
+- Kubernetes
+- Helm
+- CloudNative PG Operator
+
+## Parameters
+
+See the [values files](values.yaml).