docs: sync README and CONTRIBUTING

This is the first stable release of Postgres-to-R2 Backup.

### ✨ Key Features
- Automated PostgreSQL backups using `pg_dump`
- S3-compatible object storage support (Cloudflare R2, AWS S3, Wasabi, Backblaze B2, MinIO)
- Optional gzip compression or 7z encryption with password
- Backup retention with automatic cleanup
- Supports private and public database URLs
- UTC-based scheduling for consistent behavior across platforms

### 🐳 Docker & Deployment
- Multi-stage Docker build using Python 3.12
- Prebuilt Docker image support (`.tar` / `.tar.gz`)
- Designed for Railway deployment with cron support
- Works on VPS, Docker, and other PaaS providers

### 📄 Documentation & DX
- Expanded README with Docker, Railway, and S3 usage
- Added `.env.example` for easier configuration
- Added CONTRIBUTING guidelines

This release is production-ready and safe for existing users.

CONTRIBUTING

@@ -1,7 +1,7 @@
 # Contributing to Postgres-to-R2 Backup
 
 Thanks for your interest in contributing 🎉  
-All contributions are welcome — bug reports, documentation improvements, and code changes.
+All contributions are welcome — including bug reports, documentation improvements, and code changes.
 
 ---
 
@@ -12,6 +12,9 @@ All contributions are welcome — bug reports, documentation improvements, and c
 3. Create a feature branch from `main`
 4. Submit a pull request against `main`
 
+> `main` is considered stable and production ready.
+> Please open an issue before submitting new features or behavior changes.
+
 ---
 
 ## Development

README.md

@@ -19,7 +19,7 @@ Designed specifically as a **Railway deployment template**, with built-in suppor
 - 🔐 **Optional Encryption** — gzip compression or 7z encryption with password  
 - ☁️ **Cloudflare R2 Integration** — seamless S3-compatible storage support
 - 🧹 **Retention Policy** — automatically delete old backups  
-- 🔗 **Flexible Database URLs** — supports private and public PostgreSQL URLs  
+- 🔗 **Flexible Database URLs** — supports private and public PostgreSQL connection URLs
 - ⚡ **Optimized Performance** — parallel pg_dump and multipart S3 uploads
 - 🐳 **Docker Ready** — portable, lightweight container  
 - 🚀 **Railway Template First** — no fork required for normal usage  
@@ -109,6 +109,9 @@ You can configure the backup schedule using **Railway Cron Jobs**:
 - Use https://crontab.guru to validate expressions
 - Adjust `MAX_BACKUPS` to match your schedule
 
+> If you use Railway Cron Jobs, the service will start once per execution.
+> In this case, the internal scheduler is ignored after startup.
+
 ---
 
 ## 🖥️ Running Locally or on Other Platforms
@@ -207,6 +210,12 @@ Fork this repository **only if you plan to**:
 
 ---
 
+## ❓ FAQ
+
+**Why only DATABASE_URL?**  
+This matches how most modern platforms expose PostgreSQL credentials.  
+Support for separate DB variables may be added if there is demand.
+
 ## 📜 License
 
 This project is open source under the **MIT License**.