docs: define extraInitContainers (#5385)

Otherwise custom values will not be picked up by Flux/Helm

ci/helm-chart/values.yaml

@@ -147,6 +147,25 @@ extraContainers: |
 #  - name: DOCKER_DRIVER
 #    value: "overlay2"
 
+extraInitContainers: |
+# - name: customization
+#   image: {{ .Values.image.repository }}:{{ .Values.image.tag }}
+#   imagePullPolicy: IfNotPresent
+#   env:
+#     - name: SERVICE_URL
+#       value: https://open-vsx.org/vscode/gallery
+#     - name: ITEM_URL
+#       value: https://open-vsx.org/vscode/item
+#   command:
+#     - sh
+#     - -c
+#     - |
+#       code-server --install-extension ms-python.python
+#       code-server --install-extension golang.Go
+#   volumeMounts:
+#     - name: data
+#       mountPath: /home/coder
+
 ## Additional code-server secret mounts
 extraSecretMounts: []
   # - name: secret-files