Flesh out the readme

... slightly.

Author: ollef

README.md

@@ -1,3 +1,10 @@
 # elm-syntax
 
-Library for generating Elm syntax from Haskell in a scope-safe way.
+A library for generating Elm syntax from Haskell in a scope-safe way.
+
+This library has two main parts:
+
+* It defines abstract syntax trees (ASTs) for Elm definitions, expressions, patterns,
+and types, using the (bound library)[http://hackage.haskell.org/package/bound]
+for scope-safe local names.
+* It defines pretty printers from the ASTs to syntactically correct Elm code.