Add README for Jenkins Shared Library: Docker Build & Push Steps

README.md

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+# Jenkins Shared Library: Docker Build & Push Steps
+
+This Jenkins shared library provides reusable steps for building and pushing Docker images from your pipelines.
+
+## 📦 Included Steps
+
+| Step          | Description                            |
+|---------------|----------------------------------------|
+| `dockerBuild` | Builds a Docker image                  |
+| `dockerPush`  | Pushes a Docker image to a registry    |
+
+Each step is implemented as a Global Variable, making them directly usable in declarative pipelines.
+
+---
+
+## 🧩 How to Set Up in Jenkins
+
+### 1. Push the Library to a Git Repository
+
+Host this repository in a Git server accessible to your Jenkins instance (e.g. GitHub, GitLab, Gitea, etc.).
+
+---
+
+### 2. Register the Library in Jenkins
+
+Go to **Manage Jenkins → Configure System → Global Pipeline Libraries**, then click **Add**.
+
+Fill in the following:
+
+- **Name**: `mylib` (or any name you'd like to reference in Jenkinsfiles)
+- **Default version**: `main` (or specify a tag/branch)
+- **Retrieval method**: Modern SCM
+- **Source Code Management**: Git
+  - **Project Repository**: `https://your.git.repo/jenkins-shared-library.git`
+  - **Credentials**: (only if private)
+
+Click **Save**.
+
+---
+
+## ✅ How to Use in Your Jenkinsfile
+
+In any Jenkins pipeline, include the shared library using `@Library` and then call the steps:
+
+```groovy
+@Library('mylib') _
+
+pipeline {
+    agent any
+
+    environment {
+        DOCKER_REGISTRY = 'your.registry.example.com'
+        IMAGE_NAME = 'your/image-name'
+        IMAGE_TAG = "${DOCKER_REGISTRY}/${IMAGE_NAME}:${params.BUILD_ID}"
+    }
+
+    parameters {
+        string(name: 'BUILD_ID', defaultValue: 'latest', description: 'Docker image tag')
+    }
+
+    stages {
+        stage('Build Docker Image') {
+            steps {
+                dockerBuild(
+                    imageName: "${IMAGE_TAG}",
+                    dockerfile: "deployments/docker/Dockerfile",
+                    context: "deployments/docker"
+                )
+            }
+        }
+
+        stage('Push Docker Image') {
+            steps {
+                dockerPush(
+                    imageName: "${IMAGE_TAG}",
+                    registry: "${DOCKER_REGISTRY}",
+                    credentialsId: "your-docker-credentials-id"
+                )
+            }
+        }
+    }
+}