Update readme with required text for Amazon affiliate links

README.md

@@ -6,7 +6,7 @@ This repository contains code for the book Deep Learning with PyTorch by Eli Ste
 
 The Manning site for the book is: https://www.manning.com/books/deep-learning-with-pytorch
 
-The book can also be purchased on Amazon: https://amzn.to/38Iwrff (affiliate link)
+The book can also be purchased on Amazon: https://amzn.to/38Iwrff (affiliate link; as per the rules: "As an Amazon Associate I earn from qualifying purchases.")
 
 The errata for the book can be found on the manning website, or at https://deep-learning-with-pytorch.github.io/dlwpt-code/errata.html