Update README with comprehensive documentation for all Azure modules

[Copilot]

This PR addresses the need to document all recently added Azure infrastructure modules in the repository's README file. The previous README was minimal (only 3 lines) and didn't provide any guidance about the available modules.

Changes Made

Expanded README from 3 lines to 115 lines with comprehensive documentation including:

• Repository overview explaining the purpose and scope of the Azure Verified Modules collection

• Complete module documentation for all 4 infrastructure modules:

  • ASE (Azure App Service Environment) - Isolated App Service hosting with custom networking
  • DNS Resolution Testing - Demonstrates private endpoint DNS challenges and solutions
  • Managed Runners - GitHub Actions self-hosted runner infrastructure
  • Star Hub-Spoke Network - Enterprise network topology with central hub architecture

• Usage instructions with actual deployment commands extracted from each module's cheatsheet

• Architecture guidance including benefits, considerations, and trade-offs

• Getting started section with prerequisites and deployment workflow

• Repository structure diagram for easy navigation

• Contributing guidelines for future module additions

Key Features

• Consistent formatting with emojis and structured sections for easy scanning
• Cross-references to existing detailed READMEs in dns/ and starhubspoke/ modules
• Practical examples showing how to deploy each module
• Architecture context explaining when and why to use each pattern

The README now serves as a comprehensive guide that helps users easily find and understand the purpose of each module, addressing the core requirement to document recent folder additions.

Fixes #22.

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