Merge pull request #978 from bitring/docs/build

add example for building cloudimage from helm

docs/4.0/build-example-ingress-helm.md

@@ -0,0 +1,51 @@
+# Example for build a CloudImage from helm
+
+This is an example for build nginx-ingress CloudImage using helm.
+
+## Download helm chart
+
+```shell script
+mkdir ingress-nginx && cd ingress-nginx
+helm repo add ingress-nginx https://kubernetes.github.io/ingress-nginx
+helm pull ingress-nginx/ingress-nginx
+```
+
+Then you will got the chart:
+```shell script
+root@iZj6ceuntkc5q5p95bbqb8Z:~/nginx-ingress# ls
+ingress-nginx-4.1.0.tgz
+```
+
+## Add image list
+
+sealos will download images in image list, and cache it into registry dir.
+The dir must be `images/shim/[your image list filename]`
+
+```shell script
+root@iZj6ceuntkc5q5p95bbqb8Z:~/nginx-ingress# cat images/shim/nginxImages 
+k8s.gcr.io/ingress-nginx/controller:v1.2.0
+k8s.gcr.io/ingress-nginx/kube-webhook-certgen:v1.1.1
+```
+
+
+## Add a Dockerfile
+
+```shell script
+root@iZj6ceuntkc5q5p95bbqb8Z:~/nginx-ingress# cat Dockerfile 
+FROM scratch
+COPY . .
+CMD ["helm install ingress-nginx ingress-nginx-4.1.0.tgz --namespace ingress-nginx --create-namespace"]
+```
+
+## Build it
+
+```shell script
+sealos build -f Dockerfile -t docker.io/fanux/ingress-nginx:v1.2.0 .
+```
+
+Then push it into registry
+
+```shell script
+sealos login docker.io
+sealos push docker.io/fanux/ingress-nginx:v1.2.0
+```