README: Fix broken docs link
README: Fix broken docs link

flatpak/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,flatpak/flatpak,handsome-feng/flatpak,flatpak/flatpak,flatpak/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,handsome-feng/flatpak