add build examples

[kakaZhou719]

use this repo , user can easily build a customize rootfs. we need add a build scripts here for example show.

[bxy4543]

All dependent files are synced using github (excluding binaries). Add an automated build script under the rootfs repository, all text dependencies are provided by the rootfs repository, and the binary uses oss. step:

1. Automated Build Script Features:

• Support the specified cluster image k8s version
• k8s version 1.20 or above to below version 1.24 supports specifying cri as docker or containerd
• Support custom build name
• Supports specifying the build image architecture
• Support to specify whether to push the image after the build is completed, need to log in or specify the warehouse username and password

2. Modify the execution process of the automated build clusterimage action: git pulls the rootfs repository code, and then executes the auto-build script.

3. Updated auto-build script descriptions in all documentation.

[ricardolrl]

能不能给下完成的自定义构建步骤 目前构建报错很多 比如 我要使用本地的k8s组件或者个人仓库的k8s组件构建出一个clusterimage，具体的步骤流程应该是什么