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/doc/advanced/third-party-tools.zh-cn.md

@@ -14,23 +14,26 @@ menu:
 ---
 
 # 第三方工具列表
+
 **注意:** 这些工具并没有经过Gitea的检验，在这里列出它们只是为了便捷.
 
 *此列表并不是完整的列表，可以随时咨询如何添加!*
 
 ### 持续集成
-[BuildKite 连接器](https://github.com/techknowlogick/gitea-buildkite-connector)  
-[Jenkins 插件](https://github.com/jenkinsci/gitea-plugin)  
+
+[BuildKite 连接器](https://github.com/techknowlogick/gitea-buildkite-connector)
+[Jenkins 插件](https://github.com/jenkinsci/gitea-plugin)
 [Gitea搭配Drone](https://docs.drone.io/installation/gitea)
 
-
 ### 迁移
-[Gitea安装脚本](https://git.coolaj86.com/coolaj86/gitea-installer.sh)  
+
+[Gitea安装脚本](https://git.coolaj86.com/coolaj86/gitea-installer.sh)
 [GitHub迁移](https://gitea.com/gitea/migrator)
 
-
 ### 移动端
+
 [安卓客户端GitNex](https://gitlab.com/mmarif4u/gitnex)
 
-###  编辑器扩展
- - [Gitea的Visual Studio扩展](https://github.com/maikebing/Gitea.VisualStudio)    从   [Visual Studio 扩展市场](https://marketplace.visualstudio.com/items?itemName=MysticBoy.GiteaExtensionforVisualStudio) 下载
+### 编辑器扩展
+
+- [Gitea的Visual Studio扩展](https://github.com/maikebing/Gitea.VisualStudio)    从   [Visual Studio 扩展市场](https://marketplace.visualstudio.com/items?itemName=MysticBoy.GiteaExtensionforVisualStudio) 下载