Update README.md

Author: Billy Ellis

Diff for: README.md

@@ -28,6 +28,6 @@ These binaries are all built as ARMv7 Mach-O executables (unless specified other
 
 ## Help & Guidance
 
-Write-ups/explanations on some of the binaries can be found on [my website](http://billyellis.net) or on either one of my YouTube channels [here](https://youtube.com/c/BillyEllis) and [here](https://www.youtube.com/channel/UCspPUCzEZtMXVK0m3yrh2Zw).
+Write-ups/explanations on some of the binaries can be found on my YouTube channel [here](https://youtube.com/c/BillyEllis) or in my book [Beginner's Guide to Exploitation on ARM](http://zygosec.com/Products/).
 
 If you have any questions or requests for future exploitation challenges, tweet me [@bellis1000](https://twitter.com/bellis1000)