Add standard header to the ‘Path’ module

The header is nice to have, it's displayed in Haddocks.

src/Path.hs

@@ -1,3 +1,14 @@
+-- |
+-- Module      :  Path
+-- Copyright   :  © 2015–2016 FP Complete
+-- License     :  BSD 3 clause
+--
+-- Maintainer  :  Chris Done <chrisdone@fpcomplete.com>
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- Support for well-typed paths.
+
 {-# LANGUAGE TemplateHaskell #-}
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE EmptyDataDecls #-}