Revamp README and expand documentation (badges, examples, integrations)

[asukhodko]

Motivation

• Prepare the project for PyPI/consumer discovery by adding repository and PyPI badges and stronger SEO-friendly copy to the README.
• Make the library’s purpose and benefits clearer and more “product-led” for users seeking a semantic Markdown chunker for RAG/LLM workflows.
• Provide more usage examples and integration guidance to ease migration from the previous plugin and to show common workflows.

Description

• Reworked README.md: added GitHub/PyPI/license/download badges, stronger marketing/SEO description, reorganized sections, and expanded usage examples and presets.
• Added docs/overview.md and updated docs under docs/ including quickstart.md, config.md, strategies.md, renderers.md, debug_mode.md, and integration guides for Dify, n8n, and Windmill with concrete code snippets.
• Clarified hierarchical chunking and renderer usage, added recommended ChunkerConfig presets and adaptive sizing example, and documented Dify migration mappings and parity test commands.

Testing

• No automated tests were executed because this is a documentation-only change.
• Baseline/compatibility test commands are documented for users to run: pytest tests/baseline/test_canonical.py -v and pytest tests/baseline/test_view_level.py -v.

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Codex Task