add free ebook notification

README.md

@@ -74,3 +74,7 @@ Click on following link to see the Code in Action:
 **Rafal Leszko**
 is a passionate software developer, trainer, and conference speaker living in Krakow, Poland. He has spent his career writing code, designing architecture, and is a tech leader in a number of companies and organizations, including Hazelcast, Google, and CERN. Always open to new challenges, he has given talks and conducted workshops at numerous international conferences, including Devoxx and Voxxed Days.
 
+### Download a free PDF
+
+ <i>If you have already purchased a print or Kindle version of this book, you can get a DRM-free PDF version at no cost.<br>Simply click on the link to claim your free PDF.</i>
+<p align="center"> <a href="https://packt.link/free-ebook/9781803237480">https://packt.link/free-ebook/9781803237480 </a> </p>