Switch language name 'zh' to 'zh-cn'

This is the first step to rename 'zh' to 'zh-cn'. There are several reasons why we rename the language name.

- The upstream docsy theme changed the language name, leading to many warnings during site build;
  The side-effect is that the i18n strings are no longer working.
- We believe renaming the language is the right thing to do, because this move can make room for other variants of Chinese language, such as 'zh-tw', 'zh-sg' etc.

There would be several follow-ups to this PR, such as fixing the intra-site links, adding redirects etc.

We will lock up changes to zh/zh-cn pages for the moment, until this one gets in.

This PR is based on commit cdad0a7342.

content/zh-cn/docs/contribute/generate-ref-docs/kubernetes-components.md

@@ -0,0 +1,50 @@
+---
+title: 为 Kubernetes 组件和工具生成参考文档
+content_type: task
+weight: 120
+---
+<!--
+title: Generating Reference Pages for Kubernetes Components and Tools
+content_type: task
+weight: 120
+-->
+
+<!-- overview -->
+
+<!--
+This page shows how to build the Kubernetes component and tool reference pages.
+-->
+
+本页面描述如何构造 Kubernetes 组件和工具的参考文档。
+
+## {{% heading "prerequisites" %}}
+
+<!--
+Start with the [Prerequisites section](/docs/contribute/generate-ref-docs/quickstart/#before-you-begin)
+in the Reference Documentation Quickstart guide.
+-->
+阅读参考文档快速入门指南中的[准备工作](/zh/docs/contribute/generate-ref-docs/quickstart/#before-you-begin)节。
+
+<!-- steps -->
+
+<!--
+Follow the [Reference Documentation Quickstart](/docs/contribute/generate-ref-docs/quickstart/)
+to generate the Kubernetes component and tool reference pages.
+-->
+按照[参考文档快速入门](/zh/docs/contribute/generate-ref-docs/quickstart/)
+指引，生成 Kubernetes 组件和工具的参考文档。
+
+## {{% heading "whatsnext" %}}
+
+<!--
+* [Generating Reference Documentation Quickstart](/docs/contribute/generate-ref-docs/quickstart/)
+* [Generating Reference Documentation for kubectl Commands](/docs/contribute/generate-ref-docs/kubectl/)
+* [Generating Reference Documentation for the Kubernetes API](/docs/contribute/generate-ref-docs/kubernetes-api/)
+* [Contributing to the Upstream Kubernetes Project for Documentation](/docs/contribute/generate-ref-docs/contribute-upstream/)
+-->
+
+* [生成参考文档快速入门](/zh/docs/contribute/generate-ref-docs/quickstart/) 
+* [为 kubectll 命令生成参考文档](/zh/docs/contribute/generate-ref-docs/kubectl/)
+* [为 Kubernetes API 生成参考文档](/zh/docs/contribute/generate-ref-docs/kubernetes-api/)
+* [为上游 Kubernetes 项目做贡献以改进文档](/zh/docs/contribute/generate-ref-docs/contribute-upstream/)
+