add $5 campaign

README.md

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+## $5 Tech Unlocked 2021!
+[Buy and download this Book for only $5 on PacktPub.com](https://www.packtpub.com/product/computer-vision-with-opencv-3-and-qt5/9781788472395)
+-----
+*If you have read this book, please leave a review on [Amazon.com](https://www.amazon.com/gp/product/178847239X).     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.__*
+
 # Computer Vision with OpenCV 3 and Qt5
 This is the code repository for [Computer Vision with OpenCV 3 and Qt5](https://www.packtpub.com/application-development/computer-vision-opencv-3-and-qt5?utm_source=github&utm_medium=repository&utm_campaign=9781788472395), 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.
 ## About the Book