Added some directives about using stack to manually install IHaskell, and how to deal with the libiconv issue in OS X.

Correct filename to that which exists in master branch of the repo.

Brew says: 
```
$ brew install haskell-platform
Error: No available formula for haskell-platform
We no longer package haskell-platform. Consider installing ghc
and cabal-install instead:
  brew install ghc cabal-install

A binary installer is available:
  https://www.haskell.org/platform/mac.html
```