docs: fix NixOS link
docs: fix NixOS link

bastimeyer/streamlink,streamlink/streamlink,melmorabity/streamlink,chhe/streamlink,streamlink/streamlink,gravyboat/streamlink,melmorabity/streamlink,beardypig/streamlink,gravyboat/streamlink,chhe/streamlink,beardypig/streamlink,bastimeyer/streamlink