docs: add color-scheme

[sadeghbarati]

resolves #191

https://developer.mozilla.org/en-US/docs/Web/CSS/color-scheme

I think it's worth to add Dark mode link to the side navbar

---

Vite/Vue useDark

:root {
  color-scheme: light;
}

html.dark {
  color-scheme: dark;
}

Nuxt @nuxtjs/color-mode

html.light-mode {
  color-scheme: light;
}

html.dark-mode {
  color-scheme: dark;
}

[zernonia]

Nicely done @sadeghbarati !