Added Deep Learning with R, Second Edition

Hi,

Stjepan from Manning here. I thought this title might be a good match for your list. Thank you for considering it.

Best,

README.md

@@ -51,6 +51,7 @@
 18. [Deep Learning with Python, Second Edition](https://www.manning.com/books/deep-learning-with-python-second-edition) - by François Chollet
 19. [Evolutionary Deep Learning](https://www.manning.com/books/evolutionary-deep-learning) - by Micheal Lanham
 20. [Engineering Deep Learning Platforms](https://www.manning.com/books/engineering-deep-learning-platforms) - by Chi Wang and Donald Szeto
+21. [Deep Learning with R, Second Edition](https://www.manning.com/books/deep-learning-with-r-second-edition) - by François Chollet with Tomasz Kalinowski and J. J. Allaire
  
 ### Courses