mdoc-quickstart: Request: add dark-mode screenshot for dark-mode users

[adiabatic]

I tend to use dark mode on all my computers when the sun goes down. While this makes GitHub more pleasant to read after dark, bright-white images can be blinding. Would you consider replacing mdoc-examples.png with a dark version, or having the browser choose with something like the following?

<picture>
 <source srcset='mdoc-examples-dark.png' media='(prefers-color-scheme: dark)' type='image/png'>
 <img src='mdoc-examples-light.png' alt='Image of the mdoc-examples.7 man page'>
</picture>

I'd happily supply a pair of my own, but macOS' own manual page displayer is in monochrome, which is surprisingly less interesting than what Gentoo generates.

[flexibeast]

Well, the colours in that image are mainly the result of the settings of my terminal (kitty), rather than a Gentoo thing - i prefer strong-contrast-black-on-white at all times of day. But i'm certainly happy to change my terminal settings temporarily to generate a 'dark' version, and then try replacing the current line of Markdown referencing that image with some colour-scheme-sensitive HTML.