flatpak installation notes

[fastrizwaan]

Hi, I've included subliminal in mpv flatpak, please add instructions for flatpak mpv. https://github.com/flathub/io.mpv.Mpv/issues/66

Kindly include this in your Readme.md for io.mpv.Mpv flatpak support

cd /tmp
git clone https://github.com/davidde/mpv-autosub.git
cd mpv-autosub/
sed "s/local subliminal = .*$/local subliminal = '\/app\/bin\/subliminal/g" -i autosub.lua 
mkdir -p ~/.var/app/io.mpv.Mpv/config/mpv/scripts/
cp autosub.lua ~/.var/app/io.mpv.Mpv/config/mpv/scripts/
flatpak --user override --filesystem=host io.mpv.Mpv ; # to download subtitles in the same directory containing video