docs: add argocd-extension-installer patch example

Signed-off-by: Leonardo Luz Almeida <[email protected]>

README.md

@@ -41,8 +41,40 @@ in Argo CD API server. This process can be automated by using the
 init container that will download, extract and place the file in the
 correct location.
 
-
-
+The yaml file below is an example of how to define a kustomize patch
+to install this UI extension:
+
+```yaml
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: argocd-server
+spec:
+  template:
+    spec:
+      initContainers:
+        - name: extension-metrics
+          image: ext-installer:local
+          env:
+          - name: EXTENSION_URL
+            value: https://github.com/argoproj-labs/argocd-extension-metrics/releases/download/v1.0.0/extension.tar.gz
+          - name: EXTENSION_CHECKSUM_URL
+            value: https://github.com/argoproj-labs/argocd-extension-metrics/releases/download/v1.0.0/extension_checksums.txt
+          volumeMounts:
+            - name: extensions
+              mountPath: /tmp/extensions/
+          securityContext:
+            runAsUser: 1000
+            allowPrivilegeEscalation: false
+      containers:
+        - name: argocd-server
+          volumeMounts:
+            - name: extensions
+              mountPath: /tmp/extensions/
+      volumes:
+        - name: extensions
+          emptyDir: {}
+```
 
 ## Contributing