add $5 campaign

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/hands-on-music-generation-with-magenta/9781838824419)
+-----
+*If you have read this book, please leave a review on [Amazon.com](https://www.amazon.com/gp/product/1838824413).     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.__*
+
 # Hands-On Music Generation with Magenta
 
 [![Magenta Version 1.1.7](./docs/magenta-v1.1.7-badge.svg)](https://github.com/magenta/magenta/releases/tag/1.1.7)