Add markdownlint (#20512)

Add `markdownlint` linter and fix issues. Config is based on the one
from electron's repo with a few rules relaxed.

docs/content/page/index.zh-cn.md

@@ -47,22 +47,22 @@ Gitea的首要目标是创建一个极易安装，运行非常快速，安装和
 
 ## 组件
 
-* Web框架： [Chi](http://github.com/go-chi/chi)
-* ORM: [XORM](https://xorm.io)
-* UI 框架：
-  * [jQuery](https://jquery.com)
-  * [Fomantic UI](https://fomantic-ui.com)
-  * [Vue2](https://vuejs.org)
-  * 更多组件参见 package.json
-* 编辑器：
-  * [CodeMirror](https://codemirror.net)
-  * [EasyMDE](https://github.com/Ionaru/easy-markdown-editor)
-  * [Monaco Editor](https://microsoft.github.io/monaco-editor)
-* 数据库驱动：
-  * [github.com/go-sql-driver/mysql](https://github.com/go-sql-driver/mysql)
-  * [github.com/lib/pq](https://github.com/lib/pq)
-  * [github.com/mattn/go-sqlite3](https://github.com/mattn/go-sqlite3)
-  * [github.com/denisenkom/go-mssqldb](https://github.com/denisenkom/go-mssqldb)
+- Web框架： [Chi](http://github.com/go-chi/chi)
+- ORM: [XORM](https://xorm.io)
+- UI 框架：
+  - [jQuery](https://jquery.com)
+  - [Fomantic UI](https://fomantic-ui.com)
+  - [Vue2](https://vuejs.org)
+  - 更多组件参见 package.json
+- 编辑器：
+  - [CodeMirror](https://codemirror.net)
+  - [EasyMDE](https://github.com/Ionaru/easy-markdown-editor)
+  - [Monaco Editor](https://microsoft.github.io/monaco-editor)
+- 数据库驱动：
+  - [github.com/go-sql-driver/mysql](https://github.com/go-sql-driver/mysql)
+  - [github.com/lib/pq](https://github.com/lib/pq)
+  - [github.com/mattn/go-sqlite3](https://github.com/mattn/go-sqlite3)
+  - [github.com/denisenkom/go-mssqldb](https://github.com/denisenkom/go-mssqldb)
 
 ## 软件及服务支持