This commit introduces extensive documentation for the `springboot-async-example` module, aimed at users from beginner to advanced levels.Key changes include:1.  **Inline Comments in Java Source Files:**    *   `SpringbootAsyncApplication.java`: Detailed explanations of Spring Boot setup, `@EnableAsync`, and custom thread pool configuration.    *   `model/User.java`: Comments on the DTO structure, including field explanations and Jackson annotations.    *   `service/GitHubLookupService.java`: In-depth commentary on the `@Async` service method, `CompletableFuture`, `RestTemplate` usage, logging, and error handling considerations. All comments are tailored for beginner, intermediate, and advanced understanding.2.  **POM.xml Documentation:**    *   Added comments explaining the structure of `pom.xml`, the role of `spring-boot-starter-parent`, individual dependencies, and the `spring-boot-maven-plugin`.3.  **Application.properties Documentation:**    *   Provided explanations on the purpose of `application.properties`.    *   Added commented-out examples and explanations for configuring the asynchronous task executor via properties, even though the project uses a programmatic approach.4.  **Concepts.md File Creation:**    *   Created a new `concepts.md` file in the `springboot-async-example` root directory.    *   This file provides a structured guide covering:        *   Introduction and high-level overview of the project.        *   Basic concepts (What is Spring Boot, Asynchronous Programming, `@Async`, `CompletableFuture`).        *   Intermediate concepts (Enabling async, thread management, `TaskExecutor` configuration, `RestTemplate`).        *   Advanced concepts (Detailed `TaskExecutor` customization, error handling, `CompletableFuture` composition, testing, and pitfalls).    *   Each concept is explained with definitions, analogies, code references from the project, and best practices.This documentation aims to make the `springboot-async-example` module highly accessible and educational for developers at all skill levels, fulfilling the requirements of the original issue for this specific module.