Note stable state of 0-6 in README

Author: marijnh

README.md

@@ -4,9 +4,9 @@ These are the sources used to build the second edition of Eloquent
 JavaScript.
 
 The rewrite is a work in progress. Feedback welcome, in the form of
-issues and pull requests, but don't waste too much time on detailed
-correction of the current content yet, since large chunks might still
-be overhauled in the near future.
+issues and pull requests. Chapter 0 to 6 are in a more or less stable
+state. Don't waste too much time on detailed correction of anything
+beyond that yet.
 
 ## Building