Add Chinese support (#13)

# Main changes and Some notices

- Chines Docs should be put into corresponding versions' folders under `i18n/zh-cn/docusaurus-plugin-content-docs`. See [translate-markdown-files](https://docusaurus.io/docs/i18n/tutorial#translate-markdown-files) for reference. And also [srs-docs](https://github.com/ossrs/srs-docs) is a project that can be used as a reference. So changed the related paths in `loop_docs*` scripts.

- The markdown files under `docs/<version>` and `i18n/zh-cn/docusaurus-plugin-content-docs/<version>` must have the same name to be referred as translated. Files inside docs are corresponding to `current` version.
For example, `docs/administration/mail-templates.md` and `i18n/zh-cn/docusaurus-plugin-content-docs/current/administration/mail-templates.md`.  Filename of `mail-templates.md` must be the same (cannot be `mail-templates.zh-cn.md` and `mail-templates.us-en.md`)
So trim the `.en-us.md` and `.zh-cn.md` to `.md` to ensure the same names inside `loop_docs*` scripts.

- Used `npx docusaurus write-translations --locale zh-cn` to do sidebar, footer, and header translations, so no need to keep `sideBarCN` anymore. [reference](https://docusaurus.io/docs/cli#docusaurus-write-translations-sitedir)

- Local Tests for `en` and `zh-cn` are separeted, run the following on local respectly to test them

    ```bash
    # test en version
    npm run start
    # test zh-cn version
    npm run start -- --locale zh-cn
    ```

- If wants to test `en` and `zh-cn` both at the same time, run build and serve

    ```
    npm run build
    npm run serve
    ```

- Added some indexed page, for example:

![Screen Shot 2023-05-26 at 13.49.34](/attachments/9eeb3d38-c309-457d-9015-053b9c5ca8d6)

![Screen Shot 2023-05-26 at 13.49.49](/attachments/fc348d17-ce4c-4c4d-9240-b69add4ef06e)

Reviewed-on: https://gitea.com/gitea/gitea-docusaurus/pulls/13
Co-authored-by: HesterG <hestergong@gmail.com>
Co-committed-by: HesterG <hestergong@gmail.com>

sidebars.js

@@ -1,146 +1,87 @@
 module.exports = {
-  defaultSidebar: [
+  docs: [
     {
-      type: 'link',
+      type: 'doc',
+      id: 'intro',
       label: 'What is Gitea?',
-      href: '/next/'
     },
     {
       type: 'category',
       label: 'Installation',
+      link: {
+        "type": "generated-index"
+      },
       items: [
-          {
+        {
           type: 'autogenerated',
           dirName: 'installation',
-          }
+        }
       ]
     },
     {
       type: 'category',
       label: 'Administration',
+      link: {
+        "type": "generated-index"
+      },
       items: [
-          {
+        {
           type: 'autogenerated',
           dirName: 'administration',
-          }
+        }
       ]
     },
     {
       type: 'category',
       label: 'Usage',
+      link: {
+        "type": "generated-index"
+      },
       items: [
-          {
-            type: 'autogenerated',
-            dirName: 'usage',
-          }
+        {
+          type: 'autogenerated',
+          dirName: 'usage',
+        }
       ]
     },
     {
       type: 'category',
       label: 'Development',
+      link: {
+        "type": "generated-index"
+      },
       items: [
-          {
+        {
           type: 'autogenerated',
           dirName: 'development',
-          }
+        }
       ]
     },
     {
       type: 'category',
       label: 'Contributing',
+      link: {
+        "type": "generated-index"
+      },
       items: [
-          {
+        {
           type: 'autogenerated',
           dirName: 'contributing',
-          }
+        }
       ]
     },
     {
       type: 'category',
       label: 'Help',
+      link: {
+        "type": "generated-index"
+      },
       items: [
-          {
+        {
           type: 'autogenerated',
           dirName: 'help',
-          }
+        }
       ]
     },
-  ]/*,
-  siderBarCN: [
-    {
-      type: 'link',
-      label: 'Gitea是什么？',
-      href: 'zh-cn/next/'
-    },
-    {
-      type: 'category',
-      label: '安装',
-      items: [
-          {
-          type: 'autogenerated',
-          dirName: 'zh-cn/installation',
-          }
-      ]
-    },
-    {
-      type: 'category',
-      label: '管理',
-      items: [
-          {
-          type: 'autogenerated',
-          dirName: 'zh-cn/administration',
-          }
-      ]
-    },
-    {
-      type: 'category',
-      label: '使用',
-      items: [
-          {
-            type: 'category',
-            label: '软件包管理',
-            items: [
-                {
-                type: 'autogenerated',
-                dirName: 'zh-cn/usage/packages',
-                }
-            ]
-          },
-          {
-            type: 'autogenerated',
-            dirName: 'zh-cn/usage',
-          }
-      ]
-    },
-    {
-      type: 'category',
-      label: '开发',
-      items: [
-          {
-          type: 'autogenerated',
-          dirName: 'zh-cn/development',
-          }
-      ]
-    },
-    {
-      type: 'category',
-      label: '贡献',
-      items: [
-          {
-          type: 'autogenerated',
-          dirName: 'zh-cn/contributing',
-          }
-      ]
-    },
-    {
-      type: 'category',
-      label: '帮助',
-      items: [
-          {
-          type: 'autogenerated',
-          dirName: 'zh-cn/help',
-          }
-      ]
-    },
-  ],*/
+  ]
 };