add more plugin description

Author: kakzhou719

README.md

@@ -53,4 +53,71 @@ plugin and the other is the `cluster type` plugin.
 
 ## How to use
 
-see more details see [example here](plugins/example/readme.md)
+### use plugin though Kubefile
+
+Define the default plugin in Kubefile to build the image and run it.
+
+In many cases it is possible to use plugins without using Clusterfile, essentially sealer stores the Clusterfile plugin
+configuration in the Rootfs/Plugins directory before using it, so we can define the default plugin when we build the
+image.
+
+For example, build a new sealer image with plugins/example/example.yaml, only need to do is coping your plugin file
+to `plugins/` directory.
+
+Kubefile:
+
+```shell script
+FROM docker.io/sealerio/kubernetes:v1-22-15-sealerio-2
+COPY example.yaml plugins/
+```
+
+Build a Sealer Image that contains a plugin (or more plugins):
+
+```shell script
+sealer build -t kubernetes-with-plugin:v1 .
+```
+
+Run the image and the plugin will also be executed without having to define the plugin in the Clusterfile:
+`sealer run kubernetes-with-plugin:v1 -m x.x.x.x -p xxx`
+
+### use plugin though Clusterfile
+
+For example, set plugins/example/example.yaml content at clusterfile:
+
+```yaml
+apiVersion: sealer.io/v2
+kind: Cluster
+metadata:
+  name: default-kubernetes-cluster
+spec:
+  image: docker.io/sealerio/kubernetes:v1.22.15
+  ssh:
+    passwd: xxx
+  hosts:
+    - ips: [ 192.168.0.2,192.168.0.3,192.168.0.4 ]
+      roles: [ master ]
+    - ips: [ 192.168.0.5 ]
+      roles: [ node ]
+---
+apiVersion: sealer.io/v2
+kind: Plugin
+metadata:
+  name: pre_init_host
+spec:
+  type: SHELL
+  action: pre-init-host
+  scope: master
+  data: |
+    set -e;set -x
+    echo "i am pre init host plugin"
+```
+
+```shell script
+sealer apply -f Clusterfile
+```
+
+## Available plugin list
+
+| name | owner | category| link | description |
+| :-----| ----: | ----: |----: |----: |
+| example | sealer community | host type | plugins/example/example.yaml| just a little plugin example for user to quickly experience |