Simplified quickstart instructions

+1 for bin/setup.

I might be on my own here but I usually prefer Makefile since it will handle the dependency tracking a bit more elegantly than the various checks in the setup script, etc (https://github.com/thoughtbot/carnival/blob/master/bin/setup#L13, see dist/setup-config). Makefile could also provide some portability to Windows but would probably detract from using 'cabal build'.