Added one Scratch book. (#5134)

free-programming-books.md

@@ -2710,6 +2710,7 @@ Kerridge (PDF) (email address *requested*, not required)
 
 * [An Introductory Computing Curriculum Using Scratch](http://scratched.gse.harvard.edu/guide/download.html)
 * [Computer Science Concepts in Scratch](https://stwww1.weizmann.ac.il/scratch/scratch_en/)
+* [Learn to Code with Scratch](https://www.raspberrypi.org/magpi-issues/Essentials_Scratch_v1.pdf) - The MagPi magazine (PDF)
 * [Scratch Programming Playground](https://inventwithscratch.com/book/) - Al Sweigart