Rewrite README to emphasize documentation and learning deliverables

[thatonevikash]

Motivation

• Clarify that the repository delivers documentation and learning materials focused on web development.
• Make the README align with the deployed site tone and structure while removing vague or promotional phrasing.

Description

• Rewrote README.md to provide a structured overview with sections for What this repository delivers, Learning coverage, Content structure, and Purpose.
• Added explicit lists describing delivered document types, covered topics, and key content directories such as content/, courses/, and public/internals/.
• Kept the preview image reference (public/socials/preview.png) and improved clarity of language for learners at different levels.

Testing

• Verified the updated README.md content output with nl to confirm the file contents rendered as intended (succeeded).
• Performed a repository status check to ensure the change was recognized (succeeded).
• No automated test suites were required or modified for this documentation update.

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Codex Task