feat: update docs

[nadeem4]

This pull request significantly restructures and expands the documentation for the NL2SQL platform, focusing on making adapter development and supported database connectivity clearer and more comprehensive. It removes high-level architectural and indexing documentation from the main docs and replaces it with detailed, adapter-focused guides and references. The README is also removed, likely in favor of more targeted documentation.

Documentation Restructuring and Expansion:

• Removed the README.md file, which previously provided an overview, installation instructions, and architectural diagrams.
• Removed several architecture-focused documentation files, including those on adapters, data indexing, system overview, and routing strategy, to streamline the documentation and focus on adapters. [1] [2] [3] [4]

Adapter Documentation Overhaul:

• Added a new docs/adapters/development.md guide detailing how to build custom adapters, including required interfaces, compliance testing, and when to use base classes like DatasourceAdapter or BaseSQLAlchemyAdapter.
• Introduced a new docs/adapters/index.md as the main entry point for adapter documentation, listing supported SQL adapters and providing configuration examples.

Per-Adapter Documentation:

• Added or expanded detailed documentation pages for each supported adapter:
  • PostgreSQL: Features, configuration, and troubleshooting.
  • MySQL: Features, configuration, and limitations.
  • Microsoft SQL Server: Features, configuration, and requirements.
  • SQLite: Features, configuration, and usage hints.