updated nix manual link
updated nix manual link

juhp/stack,martin-kolinek/stack,martin-kolinek/stack,anton-dessiatov/stack,deech/stack,Blaisorblade/stack,juhp/stack,MichielDerhaeg/stack,AndreasPK/stack,MichielDerhaeg/stack,mrkkrp/stack,deech/stack,AndrewRademacher/stack,AndrewRademacher/stack,Fuuzetsu/stack,mrkkrp/stack,Blaisorblade/stack,anton-dessiatov/stack,Fuuzetsu/stack,AndreasPK/stack