Add database design section and schema diagram to README

Author: gunkim

README.md

@@ -1,18 +1,23 @@
 # ![RealWorld Example App using Kotlin and Spring](logo.png)
 
 > ### Kotlin + Spring Codebase
-> A comprehensive codebase featuring real world examples (CRUD, authentication, advanced patterns, etc.) that adheres to the [RealWorld](https://github.com/gothinkster/realworld-example-apps) specification and API.
+> A comprehensive codebase featuring real world examples (CRUD, authentication, advanced patterns, etc.) that adheres to
+> the [RealWorld](https://github.com/gothinkster/realworld-example-apps) specification and API.
 
-This project was developed to demonstrate a full-stack application built with Kotlin + Spring. It includes robust features such as CRUD operations, user authentication, routing, pagination, and more. The implementation strictly follows the Kotlin + Spring community style guides and best practices.
+This project was developed to demonstrate a full-stack application built with Kotlin + Spring. It includes robust
+features such as CRUD operations, user authentication, routing, pagination, and more. The implementation strictly
+follows the Kotlin + Spring community style guides and best practices.
 
-For further information on how this project interacts with various frontends and backends, please refer to the [RealWorld](https://github.com/gothinkster/realworld) repository.
+For further information on how this project interacts with various frontends and backends, please refer to
+the [RealWorld](https://github.com/gothinkster/realworld) repository.
 
 ---
 
 ## Table of Contents
 
 - [Prerequisites](#prerequisites)
 - [Project Structure](#project-structure)
+- [Database Design](#database-design)
 - [Features](#features)
 - [Configuration and Environment Variables](#configuration-and-environment-variables)
 - [Running the Application](#running-the-application)
@@ -30,15 +35,29 @@ For further information on how this project interacts with various frontends and
 
 The project is structured using a modular architecture, where each module plays a specific role:
 
-- **/api**: Contains the main application server code, including the entry point. This module implements the presentation and application layers.
+- **/api**: Contains the main application server code, including the entry point. This module implements the
+  presentation and application layers.
 - **/core**: Houses the domain layer, defining the core business logic and domain rules.
-- **/core-impl**: Provides concrete implementations for the domain logic specified in the `/core` module. This includes functionality such as CRUD operations and integration with specific frameworks.
+- **/core-impl**: Provides concrete implementations for the domain logic specified in the `/core` module. This includes
+  functionality such as CRUD operations and integration with specific frameworks.
 - **/e2e**: Maintains end-to-end test scripts and related resources.
 
 ![](/docs/module-structures.png)
 
 ---
 
+## **Database Design**
+
+
+![Schema Diagram](/docs/schema.png)
+
+Since there were no strict requirements regarding the field lengths, arbitrary sizes were chosen. To facilitate the use
+of UUIDs for domain IDs, the column was defined as `binary(16)`. Additionally, as MySQL InnoDB manages a clustered index
+by default, a dedicated primary key using `int` (4 bytes) was selected to prevent unnecessary expansion of the clustered
+index. No extra indexes have been defined at this stage in order to avoid premature optimization.
+
+---
+
 ## Features
 
 - **CRUD Operations**: Enables create, read, update, and delete functionalities.