Add Docker Hub and GHCR pre-built image information to README (#27)

* Add automated Docker image publishing to Docker Hub and GHCR

Enhanced the Docker build workflow to automatically build and push images to both Docker Hub and GitHub Container Registry on pushes to main branch.

Changes:
- Added Docker Hub and GHCR authentication steps
- Configured multi-registry image tagging (latest, branch, SHA)
- Updated health and API endpoint tests to use published images
- Added required permissions for GHCR package publishing

Required secrets: DOCKERHUB_USERNAME, DOCKERHUB_TOKEN

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Add Docker Hub and GHCR pre-built image information to README

Updated the README.md to inform users that pre-built Docker images are available for easy deployment.

Changes:
- Added "Pre-built Docker Images" section in Deployment Options
- Included Docker Hub pull command: karthiknitt/tamil-panchang-api:latest
- Included GHCR pull command: ghcr.io/karthiknitt/tamil-panchang-api:latest
- Added quick run example using Docker Hub image
- Fixed markdown linting issues (blank lines around code blocks)

Users can now quickly deploy the API without building from source.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: karthiknitt

README.md

@@ -360,6 +360,34 @@ The API returns a comprehensive JSON response with all panchang data:
 
 ## 🛠️ Deployment Options
 
+### Pre-built Docker Images
+
+This repository is available as pre-built Docker images on Docker Hub and GitHub Container Registry:
+
+**Docker Hub (Recommended):**
+
+```bash
+docker pull karthiknitt/tamil-panchang-api:latest
+```
+
+**GitHub Container Registry:**
+
+```bash
+docker pull ghcr.io/karthiknitt/tamil-panchang-api:latest
+```
+
+**Quick Run:**
+
+```bash
+# Run with Docker Hub image
+docker run -d -p 8000:8000 -p 8001:8001 karthiknitt/tamil-panchang-api:latest
+
+# Test the API
+curl http://localhost:8000/health
+```
+
+The images are automatically built and published on every push to the main branch via GitHub Actions.
+
 ### Option 1: Standalone (Local Development/Testing)
 
 **Best for:** Local development, testing, or simple deployments without reverse proxy
@@ -439,6 +467,54 @@ environment:
 
 **Note:** Swiss Ephemeris data files are automatically downloaded during Docker build.
 
+### CI/CD Pipeline
+
+This repository includes automated Docker image building and publishing via GitHub Actions.
+
+#### Automated Deployment
+
+The CI/CD pipeline automatically:
+
+1. **Triggers** on pushes to the `main` branch
+2. **Builds** the Docker image using the optimized Dockerfile
+3. **Pushes** to both Docker Hub and GitHub Container Registry (GHCR)
+4. **Tests** the deployed image to ensure functionality
+
+#### Required Secrets
+
+To enable automated publishing, configure these repository secrets in GitHub:
+
+| Secret Name | Description | Where to Get It |
+|-------------|-------------|-----------------|
+| `DOCKERHUB_USERNAME` | Your Docker Hub username | Docker Hub account settings |
+| `DOCKERHUB_TOKEN` | Docker Hub access token | Docker Hub → Account Settings → Security → Access Tokens |
+
+**Setting up Docker Hub Token:**
+
+1. Go to [Docker Hub](https://hub.docker.com/)
+2. Login and go to Account Settings → Security
+3. Generate a new Access Token
+4. Copy the token and add it as `DOCKERHUB_TOKEN` in repository secrets
+
+**Note:** GHCR publishing uses the built-in `GITHUB_TOKEN` which is automatically provided by GitHub Actions. You do **not** need to create or configure this token - it's available by default in all workflows.
+
+#### Image Names
+
+Images are published with these names:
+
+- **Docker Hub:** `yourusername/tamil-panchang-api`
+- **GHCR:** `ghcr.io/yourusername/tamil-panchang-api`
+
+Replace `yourusername` with your actual GitHub/Docker Hub username.
+
+#### Tags
+
+The following tags are automatically applied:
+
+- `latest` - Latest build from main branch
+- `main` - Current main branch commit
+- `main-<sha>` - Specific commit SHA (first 7 characters)
+
 ## 📜 Fair Use Policy
 
 This API is free for everyone: