Update README: add value proposition, reorder sections, and include project status

[asukhodko]

Motivation

• Improve README clarity and sales-readiness by adding a short value proposition under the project title.
• Reorder documentation into a consistent, consumer-friendly flow for RAG and LLM ingestion workflows.
• Surface project status, compatibility, and support information to reduce onboarding friction.
• Make each top-level section concise and benefit-focused so readers can quickly evaluate fit for their pipelines.

Description

• Added a 2–3 sentence value proposition block immediately below the repository header to summarize core benefits.
• Inserted a Table of Contents and reordered sections to: Overview → Key Features → Use Cases → Installation → Quickstart → Core Concepts → Examples → Configuration → Renderers → Integrations → FAQ → Contributing → License → Links.
• Introduced a Project Status / Compatibility / Support subsection with stability, supported Python version (3.12+), and a link to the GitHub issue tracker.
• Tightened copy across sections and cleaned up the Links and Renderers blocks to present 2–6 lines of benefit-focused content per section.

Testing

• No automated tests were executed because this is a documentation-only change.
• Local repository status was updated and the modified file committed with the message Revise README structure and messaging.
• Linting or type checks were not run as part of this change.
• Manual review confirmed Table of Contents links and new subsections are present in README.md.

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Codex Task