books: add terraform in depth

Signed-off-by: Rui Chen <rui@chenrui.dev>

README.md

@@ -81,6 +81,7 @@ Terraform enables you to safely and predictably create, change, and improve prod
 - [Terraform Best Practices](https://www.terraform-best-practices.com/) - [open-source ebook](https://github.com/antonbabenko/terraform-best-practices)
 - [Terraform Cookbook](https://www.amazon.com/Terraform-Cookbook-Efficiently-Infrastructure-platforms/dp/1800207557)
 - [Terraform in Action](https://www.manning.com/books/terraform-in-action)
+- [Terraform in Depth](https://www.manning.com/books/terraform-in-depth)
 - [Terraform: Up & Running, 3rd ed.](https://www.terraformupandrunning.com/)
 - [The Terraform Book](https://terraformbook.com/)
 - [IaC starting with Terraform(Korean)](https://product.kyobobook.co.kr/detail/S000202478097)