add free ebook notification

Author: Packt-ITService

README.md

@@ -1,2 +1,6 @@
 # Python-GUI-Programming-with-Tkinter-2E
 Python GUI Programming with Tkinter 2E.Published by Packt
+### 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/9781801815925">https://packt.link/free-ebook/9781801815925 </a> </p>