add free ebook notification

README.md

@@ -29,3 +29,7 @@ NA
 * [Node.js Developing Web Applications [Video]](https://www.packtpub.com/web-development/nodejs-developing-web-applications-video)
 
 * [React Native - The Practical Guide [Video]](https://www.packtpub.com/web-development/react-native-practical-guide-video)
+### 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/9781789135770">https://packt.link/free-ebook/9781789135770 </a> </p>