Add comprehensive README summarizing the Ostorlab Security Benchmarks repository

[Copilot]

Enhanced the main README.md to provide a comprehensive overview of the Ostorlab Security Benchmarks repository, addressing the need for clear documentation about the repository's purpose and contents.

What this PR does

The original README contained only a minimal title "Ostorlab Validation Benchmarks" without explaining what the repository is for or how to use it. This PR transforms it into a comprehensive guide that explains:

• Repository Purpose: A collection of vulnerable Android applications designed to validate mobile security analysis tools
• Complete Inventory: All 13+ security benchmarks organized by vulnerability category
• Structured Overview: Clear categorization of security vulnerabilities covered
• Usage Instructions: How to build and test the benchmarks
• Educational Value: Each benchmark demonstrates specific security flaws with detailed documentation

Repository Contents Summary

The repository contains Android security benchmarks covering major vulnerability categories:

🔐 Insecure Data Storage (4 benchmarks)

• SharedPreferences, Internal Storage, External Storage, SQLite cleartext storage

🌐 WebView Security Issues (3 benchmarks)

• JavaScript Injection, XSS via Intent Parameters, Stored XSS

🔒 Network Security (2 benchmarks)

• TLS/SSL Certificate Validation bypass, Cleartext HTTP communication

📱 Platform Security (2 benchmarks)

• Unprotected Critical Activities, Path Traversal file access

💻 Code Security (2 benchmarks)

• Hardcoded Secrets, Sensitive data in application logs

Target Audience

This documentation helps:

• Security researchers testing mobile analysis tools
• Developers learning about mobile security vulnerabilities
• Tool vendors validating their security scanning capabilities
• Educational institutions teaching mobile security

The enhanced README provides the context and guidance needed for users to understand and effectively utilize these security benchmarks.

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