Add documentation workflow for service contributors

[Cinzya]

Summary

• Adds comprehensive documentation workflow for contributors who want to add service documentation to the docs repository
• Provides step-by-step instructions for creating service documentation pages
• Includes template and formatting guidelines for consistency across service docs

Changes Made

• New section: "Adding a new service template to the Coolify Documentation" with 5-step process
• Documentation template: Standard format for service pages with frontmatter, ZoomableImage usage, and content structure
• Services overview instructions: How to add services to the main Services list component
• Minor fix: Corrected "Docker Compose" to "Docker Compose Empty" deployment option

Why This Matters

Currently, the contribution guide only covers adding service templates to the main Coolify repository. This addition helps contributors understand the complete process of documenting their services in the docs repository, ensuring users have proper documentation for newly added services.

Test Plan

• Documentation renders correctly in local development (bun run dev)
• All formatting and markdown syntax is valid
• Instructions follow the established pattern of numbered steps with clear actions

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