Update Developer Guide

Author: prankul88

docs/book/src/developer/guide.md

@@ -62,6 +62,24 @@ You'll need to [install `kubebuilder`][kubebuilder].
 
 [kubebuilder]: https://book.kubebuilder.io/quick-start.html#installation
 
+### Cert-Manager
+
+You'll need to deploy [cert-manager] components on your [management cluster][mcluster], using `kubectl`
+
+```bash
+kubectl apply -f https://github.com/jetstack/cert-manager/releases/download/v0.11.0/cert-manager.yaml
+```
+
+Ensure the cert-manager webhook service is ready before creating the Cluster API components. 
+
+This can be done by running: 
+
+```bash
+kubectl wait --for=condition=Available --timeout=300s apiservice v1beta1.webhook.cert-manager.io
+```
+
+[cert-manager]: https://github.com/jetstack/cert-manager
+
 ## Development
 
 ## Option 1: Tilt
@@ -115,7 +133,7 @@ and
 
 ```
 $EDITOR config/manager/manager_image_patch.yaml
-$EDITOR
+$EDITOR test/infrastructure/docker/config/default/manager_image_patch.yaml
 ```
 
 In both cases, change the `- image:` url to the digest URL mentioned above:
@@ -149,6 +167,7 @@ clusterrole.rbac.authorization.k8s.io/capi-manager-role configured
 rolebinding.rbac.authorization.k8s.io/capi-leader-election-rolebinding configured
 clusterrolebinding.rbac.authorization.k8s.io/capi-manager-rolebinding configured
 deployment.apps/capi-controller-manager created
+
 $ kustomize build test/infrastructure/docker/config | kubectl apply -f -
 namespace/capd-system configured
 customresourcedefinition.apiextensions.k8s.io/dockerclusters.infrastructure.cluster.x-k8s.io configured