chore: add zh-CN document (#20)

Author: yoli799480165

README.md

@@ -2,7 +2,7 @@
 
 A lib for generating Style Sheets with C#.
 
-For documentation see our [docs](./docs/index.md).
+[English](./docs/index.md) | [简体中文](./docs/index.zh-CN.md)
 
 ![Latest Version](https://img.shields.io/github/actions/workflow/status/ant-design-blazor/CssInCsharp/package.yml?style=flat-square)
 [![CssInCSharp](https://img.shields.io/nuget/v/CssInCSharp.svg?color=red&style=flat-square)](https://www.nuget.org/packages/CssInCsharp)

docs/index.md

@@ -1,3 +1,27 @@
+# Table of Contents
+- [Table of Contents](#table-of-contents)
+- [Getting Started](#getting-started)
+  - [Install Package](#install-package)
+  - [Add Using](#add-using)
+  - [Create CSS Object](#create-css-object)
+- [Usage](#usage)
+  - [Structured Stylesheet](#structured-stylesheet)
+  - [Parent Selectors](#parent-selectors)
+  - [Merge](#merge)
+    - [Reuse global styles](#reuse-global-styles)
+    - [Using merge operator](#using-merge-operator)
+    - [Overwrite existing styles](#overwrite-existing-styles)
+  - [Variables](#variables)
+    - [Retain CSS](#retain-css)
+  - [Functions](#functions)
+  - [Animation](#animation)
+  - [Colors](#colors)
+  - [Style Rendering](#style-rendering)
+  - [CSS Isolation](#css-isolation)
+  - [Custom Component Style](#custom-component-style)
+
+# Getting Started
+
 ## Install Package
 ```sh
 dotnet add package CssInCSharp
@@ -100,6 +124,7 @@ var css = new CSSObject
 }
 ```
 
+# Usage
 ## Structured Stylesheet
 
 The stylesheet is structured, this is similar to less or sass.