Update README.md

Only use new-session on systems with legacy_tiocsti enabled

#268

Rename DISABLE_LSFG env variable

Disable lsfg-vk by default

Update integrated utils

Exit with error if sha256sums.txt was not downloaded

Add ffmpegthumbnailer

Fix bash compilation with GCC 15

Add gnome-themes-extra package

Merge pull request #222 from vitaly-zdanevich/patch-13

README.md: add that can install from gentoo-zh overlay