doc: update Docker docs for OS X
doc: update Docker docs for OS X

Also move prerequisites to top and clarify.

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