Add Alibaba Cloud ECI Documents

Alibaba Cloud ECI(Elastic Container Instance) is a service that allow you
run containers without having to manage servers or clusters.

This commit add ECI documents for virtual kubelet.

Signed-off-by: xianwei.zw <xianwei.zw@alibaba-inc.com>
Signed-off-by: shidao.ytt <shidao.ytt@alibaba-inc.com>

providers/alicloud/README.md

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+# Alibaba Cloud ECI
+
+<img src="eci.svg" width="200" height="200" />
+
+Alibaba Cloud ECI(Elastic Container Service) is a service that allow you run containers without having to manage servers or clusters.
+
+You can find more infomation via [alibaba cloud ECI web portal](https://www.aliyun.com/product/eci)
+
+## Alibaba Cloud ECI Virtual-Kubelet Provider
+Alibaba ECI provider is an adapter to connect between k8s and ECI service to implement pod from k8s cluster on alibaba cloud platform
+
+## Prerequisites
+To using ECI service on alibaba cloud, you may need open ECI service on [web portal](https://www.aliyun.com/product/eci), and then the ECI service will be available
+
+## Deployment of the ECI provider in your cluster
+configure and launch virtual kubelet
+```
+export ECI_REGION=cn-hangzhou
+export ECI_SECURITY_GROUP=sg-123
+export ECI_VSWITCH=vsw-123
+export ECI_ACCESS_KEY=123
+export ECI_SECRET_KEY=123
+
+VKUBELET_TAINT_KEY=alibabacloud.com/eci virtual-kubelet --provider alicloud
+```
+confirm the virtual kubelet is connected to k8s cluster
+```
+$kubectl get node
+NAME                                 STATUS                     ROLES     AGE       VERSION
+cn-shanghai.i-uf69qodr5ntaxleqdhhk   Ready                      <none>    1d        v1.9.3
+virtual-kubelet                      Ready                      agent     10s       v1.8.3
+```
+
+## Schedule K8s Pod to ECI via virtual kubelet
+You can assign pod to virtual kubelet via node-selector and toleration.
+```
+apiVersion: v1
+kind: Pod
+metadata:
+  name: mypod
+spec:
+  nodeName: virtual-kubelet
+  containers:
+  - name: nginx
+    image: nginx
+  tolerations:
+  - key: alibabacloud.com/eci
+    operator: "Exists"
+    effect: NoSchedule
+```
+
+# Alibaba Cloud Serverless Kubernetes
+Alibaba Cloud serverless kubernetes allows you to quickly create kubernetes container applications without
+having to manage and maintain clusters and servers.  It is based on ECI and fully compatible with the Kuberentes API.
+
+You can find more infomation via [alibaba cloud serverless kubernetes product doc](https://www.alibabacloud.com/help/doc-detail/71479.htm)
+

providers/alicloud/eci.svg

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