add free ebook notification

Author: Packt-ITService

README.md

@@ -42,3 +42,7 @@ the PostgreSQL database.
 * [Tkinter GUI Application Development Blueprints](https://www.packtpub.com/application-development/tkinter-gui-application-development-blueprints?utm_source=github&utm_medium=repository&utm_campaign=9781785889738)
 
 
+### 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/9781788835886">https://packt.link/free-ebook/9781788835886 </a> </p>