Add a note that cert-manager is optional

- will add more detailed documentation about how to install without
cert-manager as part of: #73

README.md

@@ -9,9 +9,9 @@ Kubernetes operator to manage [RabbitMQ](https://www.rabbitmq.com/) messaging to
 Before deploying Messaging Topology Operator, you need to have:
 
 1. A Running k8s cluster
-2. [cert-manager](https://cert-manager.io/docs/installation/kubernetes/) `1.2.0` or above, installed in the k8s cluster
-3. RabbitMQ [Cluster Operator](https://github.com/rabbitmq/cluster-operator) installed in the k8s cluster
-4. A [RabbitMQ cluster](https://github.com/rabbitmq/cluster-operator/tree/main/docs/examples) deployed using the Cluster Operator
+2. RabbitMQ [Cluster Operator](https://github.com/rabbitmq/cluster-operator) installed in the k8s cluster
+3. A [RabbitMQ cluster](https://github.com/rabbitmq/cluster-operator/tree/main/docs/examples) deployed using the Cluster Operator
+4. (Optional) [cert-manager](https://cert-manager.io/docs/installation/kubernetes/) `1.2.0` or above, installed in the k8s cluster
 
 If you have `kubectl` configured to access your running k8s cluster, you can then run the following command to install the Messaging Topology Operator:
 
@@ -28,6 +28,10 @@ You can create RabbitMQ resources:
 5. [Vhost](./docs/examples/vhosts)
 6. [Policy](./docs/examples/policies)
 
+## Install without cert-manager
+
+If you do not have cert-manager in your k8s cluster, you need to generate certificates used by admission webhooks yourself and include them in the operator deployment, crds, and webhooks manifests.
+
 ## Contributing
 
 This project follows the typical GitHub pull request model. Before starting any work, please either comment on an [existing issue](https://github.com/rabbitmq/messaging-topology-operator/issues), or file a new one.