add $5 campaign

Author: Packt-ITService

README.md

@@ -1,3 +1,8 @@
+## $5 Tech Unlocked 2021!
+[Buy and download this Book for only $5 on PacktPub.com](https://www.packtpub.com/product/modular-programming-with-python/9781785884481)
+-----
+*If you have read this book, please leave a review on [Amazon.com](https://www.amazon.com/gp/product/1785884484).     Potential readers can then use your unbiased opinion to help them make purchase decisions. Thank you. The $5 campaign         runs from __December 15th 2020__ to __January 13th 2021.__*
+
 # Modular-Programming-with-Python