SNOW-111111: update README.md

[sfc-gh-gnugmanov]

docs: Enhance README.md with comprehensive architecture overview and service documentation

• Add detailed project overview highlighting security-first approach and zero trust architecture
• Expand service documentation with comprehensive table of all 20+ available services
• Improve getting started section with clearer prerequisites and setup instructions
• Add architecture overview section explaining core components and service patterns
• Enhance monitoring and debugging information with specific endpoints
• Restructure content for better readability and navigation
• Maintain existing technical details while improving accessibility for new users

This update provides a complete picture of SansShell's capabilities, architecture,
and usage patterns for both newcomers and experienced users.