Merge pull request kubernetes#87065 from tanjunchen/add-README-hack

add README.md in hack/

Author: k8s-ci-robot

hack/README.md

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+# Kubernetes hack GuideLines
+
+This document describes how you can use the scripts from [`hack`](.) directory 
+and gives a brief introduction and explanation of these scripts. 
+
+## Overview
+
+The [`hack`](.) directory contains many scripts that ensure continuous development of kubernetes, 
+enhance the robustness of the code, improve development efficiency, etc. 
+The explanations and descriptions of these scripts are helpful for contributors. 
+For details, refer to the following guidelines.
+
+## Key scripts
+
+* [`verify-all.sh`](verify-all.sh): This script is a vestigial redirection, Please do not add "real" logic. It is equivalent to `make verify`.
+* [`update-all.sh`](update-all.sh): This script is a vestigial redirection, Please do not add "real" logic. 
+The `true` target of this makerule is `hack/make-rules/update.sh`.It is equivalent to `make update`.
+
+## Attention
+Note that all scripts must be run from the Kubernetes root directory. 
+**We should run `hack/verify-all.sh` before submitting a PR and if anything fails run `hack/update-all.sh`**. 
+ 
+
+