Update README.md to enhance structure and clarity by adding headings and improving formatting for environment variables and project components

README.md

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 # backup-client
 
+A containerized SSH backup server built on Alpine Linux, designed to provide secure remote backup access using SSH/SFTP protocols.
+
+## Features
+
+- 🔐 **Secure SSH Access**: Automated SSH server setup with configurable authentication
+- 🐳 **Docker Ready**: Multi-architecture support (linux/amd64, linux/arm64)
+- 📦 **BorgBackup Integration**: Built-in backup solution support
+- ⚙️ **Dynamic Configuration**: Real-time SSH config monitoring and reloading
+- 🔄 **CI/CD Pipeline**: Automated builds via Drone CI
+
+## Quick Start
+
+```bash
+docker run -p 20022:20022 -v /backup/data:/home/backup safebox/backup-client
+```
+
+## Configuration
+### Environment Variables
+
+| Variable     | Default | Description                   |
+|--------------|---------|-------------------------------|
+| SSH_PORT     | 20022   | SSH server listening port     |
+| SSH_USER     | backup  | Backup user name              |
+| SSH_PASSWORD | backup  | User password for authentication |
+
+## How it Works
+The container automatically:
+
+User Setup: Creates the backup user with configured credentials
+SSH Configuration: Generates host keys (Ed25519) if not present
+Server Start: Launches SSH daemon
+
+## Key Components
+Dockerfile: Alpine-based image with OpenSSH, su-exec, and BorgBackup
+start_backup.sh: Main entrypoint script handling SSH setup 
+.drone.yml: CI/CD pipeline for multi-architecture builds
+
+Security Features
+Host Key Persistence: SSH host keys are generated once and persisted
+Configurable Authentication: Supports both password and public key authentication
+User Isolation: Runs SSH daemon as non-root user
+
+## Development
+
+Development builds: Push to registry.dev.format.hu/backup-client
+Release builds: Tag events push to safebox/backup-client on DockerHub
+Multi-architecture: Supports both AMD64 and ARM64 platforms
+
+## License
+This project is open source. Please check the license file for details.
+