dark mode announcement

main.md

Thanks to work of @avorobey we now have experimental support for dark theme.

You can get it in latest pre-release version: https://www.sumatrapdfreader.org/prerelease

To use it:

• Ctrl + K to get Command Palette
• type next theme to invoke Switch to next theme command

To report issues: sumatrapdfreader/sumatrapdf#3429