Relative local links can only be to markdown files

[ryan-blunden]

On the NGINX documentation page, there is a link to a page with the Mermaid.js markup used to render a diagram for non-sighted users.

I wanted to link straight to a nginx-diagram.mermaid file but docsite only allows relative links to .md files.

It's not a huge deal (you just create a markdown file with the diagram text), but it would be nice to be able to link to any file type.