add $5 campaign

Author: Packt-ITService

Diff for: README.md

@@ -1,3 +1,8 @@
+## $5 Tech Unlocked 2021!
+[Buy and download this product for only $5 on PacktPub.com](https://www.packtpub.com/)
+-----
+*The $5 campaign         runs from __December 15th 2020__ to __January 13th 2021.__*
+
 # Mastering JavaScript Functional Programming
 This is the code repository for [Mastering JavaScript Functional Programming](https://www.packtpub.com/web-development/mastering-javascript-functional-programming), published by [Packt](https://www.packtpub.com/?utm_source=github). It contains all the supporting project files necessary to work through the book from start to finish.