Update contributing

CONTRIBUTING.md

@@ -1,12 +1,10 @@
 The content of this wiki will be included in a forthcoming book from Chapman
 & Hall, and hence I need to own the copyright for the complete content
-of the wiki. I will make some money from the book, but it's not likely to be a 
-huge amount (probably <$10,000 over 2 years, which works out to a fairly low 
-hourly rate). The wiki will continue to be freely available and I'll acknowledge
-all contributions in the printed book.
+of the wiki. The content of this site will continue to be freely available 
+and I'll acknowledge all contributions in the printed book.
 
 To confirm that you're ok with giving me your copyright, please include the 
 phrase: "I assign the copyright of this contribution to Hadley Wickham".
 
 If you have any questions, feel free to raise them in the pull request, or 
-send me [an email](mailto:h.wickham@gmail.com).
+send me [an email](mailto:h.wickham@gmail.com).