Add project README for the Jenkins-on-Docker pipeline

[Copilot]

This repository did not include a README describing what the project does or how to use it. This change adds a focused project guide based on the existing Jenkins pipeline and helper script.

• Overview

  • Adds a top-level README.md describing the repository as a Jenkins declarative pipeline that provisions a Jenkins controller in Docker.

• Pipeline behavior

  • Documents the pipeline flow: optional cleanup of an existing container, optional pull of jenkins/jenkins:lts, container startup, and retrieval of the initial admin password.

• Operational details

  • Captures the exposed pipeline parameters (Name, Port, Stop_Existing, Pull_Latest) and the runtime assumptions for the Jenkins agent (master label, Docker at /usr/local/bin/docker).

• Usage and validation

  • Adds concise usage guidance for running the pipeline from Jenkins.
  • Documents the existing lint.sh helper for Jenkinsfile validation against a local Jenkins instance.

## Pipeline parameters

| Parameter | Default | Description |
| --- | --- | --- |
| `Name` | `jenkins` | Name of the Docker container to run. |
| `Port` | `49000` | Host port mapped to container port `8080`. |