another CTA re code

preface.asciidoc

@@ -267,6 +267,12 @@ Particularly if you're intending to apply some of these patterns in your own
 projects, then working through a simple example is a great way to get some
 safe practice.
 
+TIP: At the very least, do a `git checkout` of the code from our repo as you
+    read each chapter.  Being able to jump in and see the code in the context of
+    an actual working app will help answer a lot of questions as you go, and
+    makes everything more real.  You'll find instructions for how to do that
+    at the beginning of each chapter.
+
 
 === License