Clarified the role of the `- '.'` line.
Clarified the role of the `- '.'` line.

As mentioned in #1862 (specifically [this comment](https://github.com/commercialhaskell/stack/issues/1862#issuecomment-191173247))
MichielDerhaeg/stack,mrkkrp/stack,Fuuzetsu/stack,sjakobi/stack,narrative/stack,deech/stack,AndrewRademacher/stack,anton-dessiatov/stack,juhp/stack,martin-kolinek/stack,phadej/stack,phadej/stack,Heather/stack,juhp/stack,Blaisorblade/stack,AndreasPK/stack,narrative/stack,MichielDerhaeg/stack,deech/stack,Blaisorblade/stack,sjakobi/stack,mrkkrp/stack,martin-kolinek/stack,AndreasPK/stack,Fuuzetsu/stack,Heather/stack,AndrewRademacher/stack,anton-dessiatov/stack