Better README.

Author: athas

README.md

@@ -1,7 +1,17 @@
 # Parallel Programming in Futhark
 
 This material aims at introducing the reader to data-parallel
-functional programming using the Futhark language.
+functional programming using the Futhark language.  It is
+work-in-progress, but probably constitutes the best introduction to
+Futhark programming.
+
+## Reading the Book
+
+Navigate to
+[Releases](https://github.com/diku-dk/futhark-book/releases) and pick
+the most recent PDF file.
+
+## Writing the Book
 
 The document is compiled by typing `make` and the embedded Futhark
 code is compiled, executed, and tested by typing `make test`.