add comprehensive local setup and build instructions

[mindsparkist]

What does this PR do?

This PR updates the project documentation to include a complete, step-by-step guide for setting up the local development environment on Ubuntu. It covers all necessary dependencies to compile and run the Spring Boot application.

Changes Included:

• Added instructions for installing default-jdk and setting the JAVA_HOME environment variable.
• Added instructions for installing Apache Maven.
• Provided the exact Maven Build Lifecycle commands (mvn clean install) required to build the .jar artifact.
• Added the terminal command to run the packaged application and access it on port 8080.

Why are we doing this?

To lower the barrier to entry for new developers or contributors. Previously, the setup steps were [missing / unclear], which could lead to environment configuration issues.

How to test this:

1. Review the updated README.md for clarity and accuracy.
2. Follow the steps on a fresh Ubuntu environment to ensure the application builds and starts successfully on localhost:8080.