Add documentation for new approach(es)

[Sintrastes]

Whereas originally what I had in mind for Montague was something that could be fed into a logic programing-like solver, now it is clear that there are at least other possibilities (see the work in Montague.Experimental.Typed and related modules).

I should add some documentation outlining these different approaches, as I think they would be good examples of different potential uses for Montague.