Restructure documentation. Now the documentation has installation, administration, usage, development, contributing the 5 main parts (#23629)

- **Installation**: includes how to install Gitea and related other
tools, also includes upgrade Gitea
- **Administration**: includes how to configure Gitea, customize Gitea
and manage Gitea instance out of Gitea admin UI
- **Usage**: includes how to use Gitea's functionalities. A sub
documentation is about packages, in future we could also include CI/CD
and others.
- **Development**: includes how to integrate with Gitea's API, how to
develop new features within Gitea
- **Contributing**: includes how to contribute code to Gitea
repositories.

After this is merged, I think we can have a sub-documentation of `Usage`
part named `Actions` to describe how to use Gitea actions

---------

Co-authored-by: John Olheiser <[email protected]>

doc/installation/upgrade-from-gogs.zh-cn.md

@@ -0,0 +1,26 @@
+---
+date: "2016-12-01T16:00:00+02:00"
+title: "从 Gogs 升级"
+slug: "upgrade-from-gogs"
+weight: 10
+toc: false
+draft: false
+menu:
+  sidebar:
+    parent: "installation"
+    name: "从 Gogs 升级"
+    weight: 101
+    identifier: "upgrade-from-gogs"
+---
+
+# 从 Gogs 升级
+
+如果你正在运行Gogs 0.9.146以下版本，你可以平滑的升级到Gitea。该升级需要如下的步骤：
+
+* 停止 Gogs 的运行
+* 拷贝 Gogs 的配置文件 `custom/conf/app.ini` 到 Gitea 的相应位置。
+* 拷贝 Gitea 的 `options/` 到 Home 目录下。
+* 如果你还有更多的自定义内容，比如templates和localization文件，你需要手工合并你的修改到 Gitea 的 Options 下对应目录。
+* 拷贝 Gogs 的数据目录 `data/` 到 Gitea 相应位置。这个目录包含附件和头像文件。
+* 运行 Gitea
+* 登录 Gitea 并进入 管理面板, 运行 `重新生成 '.ssh/authorized_keys' 文件（警告：不是 Gitea 的密钥也会被删除）` 和 `重新生成所有仓库的 Update 钩子（用于自定义配置文件被修改）`。