Update DDD book links

docs/en/Domain-Driven-Design.md

@@ -32,6 +32,6 @@ DDD mostly interest in the **Domain** and the **Application** layers, rather tha
   * [Data Transfer Objects (DTOs)](Data-Transfer-Objects.md)
   * [Unit of Work](Unit-Of-Work.md)
 
-## The Ultimate DDD Implementation Guide
+## Free E-Book: Implementing DDD
 
-See the [Implementing Domain Driven Design](Domain-Driven-Design-Implementation-Guide.md) guide as a **complete reference**. The Guide explains the Domain Driven Design and introduces explicit **rules and examples** to give a deep understanding of the **implementation details**.
+See the [Implementing Domain Driven Design book](https://abp.io/books/implementing-domain-driven-design) as a **complete reference**. This book explains the Domain Driven Design and introduces explicit **rules and examples** to give a deep understanding of the **implementation details**.

docs/en/Index.md

@@ -29,8 +29,9 @@ ABP has a **comprehensive documentation** that not only explains the ABP Framewo
 ABP offers a complete, modular and layered software architecture based on [Domain Driven Design](Domain-Driven-Design.md) principles and patterns. It also provides the necessary infrastructure to implement this architecture.
 
 * See the [Modularity](Module-Development-Basics.md) document to understand the module system.
-* [Implementing Domain Driven Design](Domain-Driven-Design-Implementation-Guide.md) document is an ultimate guide for who want to understand and implement the DDD.
+* [Implementing Domain Driven Design Book](https://abp.io/books/implementing-domain-driven-design) is an ultimate guide for who want to understand and implement the DDD.
 * [Microservice Architecture](Microservice-Architecture.md) document explains how ABP helps to create a microservice solution.
+* [Multi-Tenancy](Multi-Tenancy.md) document introduces multi-tenancy and explores the ABP multi-tenancy infrastructure.
 
 ### Infrastructure
 
@@ -55,6 +56,14 @@ See the [Application Modules](Modules/Index.md) document for all pre-built modul
 
 The [Startup templates](Startup-Templates/Index.md) are pre-built Visual Studio solution templates. You can create your own solution based on these templates to **immediately start your development**.
 
+## Free E-Book: Implementing Domain Driven Design
+
+![Implementing Domain Driven Design](images/implementing-domain-driven-design-book.png)
+
+A **practical guide** for implementing Domain Driven Design (DDD). While the implementation details are **based on the ABP Framework** infrastructure, the basic concepts, principles and models can be applied to any solution, even if it is not a .NET solution.
+
+[Click here to get your free copy](https://abp.io/books/implementing-domain-driven-design).
+
 ## ABP Community
 
 ### The Source Code