Give recommendations for how to install system libraries

It'd be cool to recommend things like `sudo apt-get install libpq-dev` or even just `sudo apt-cache search libpq`. On windows, it should recommend something like `stack exec -- pacman -S ...`

From a comment on https://github.com/commercialhaskell/stack/issues/1384 by amigalemming:

> You can use the pkgconfig-depends field of Cabal for showing external
> dependencies. An automated tool could scan available packages of Ubuntu or
> Debian or MSYS/Arch for the according .pc files.