markdown export

Couldn't sort out how to add something to Trello, adding here.

# Feature request

Markdown export to existing docs (where possible).

## Summary

The idea would be to show a markdown version of a page by using the ".md" extension to url's. This would be an alternative to the HTML view.

Devdocs already has simplified views of documentation, adding an option to view documentation or export documentation in markdown view would add some additional utility. Rather than depending on a conversion from html to markdown, especially in case where a document was originally in markdown.

This would also enable a potential AI integration, where markdown is preferred.

## Examples

I came across another service having the feature: https://www.mintlify.com/docs/ai/markdown-export

该 issue 没有指出任何文件、测试或代码入口点。首先跟踪现有文档页面如何通过其 HTML URL 提供服务，然后确定在原始 Markdown 可用时，.md URL 如何公开它。完成内容应包括为现有文档定义 Markdown 导出行为，并覆盖相关的页面类型。

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