Update README.md for Diffbot

[CognigyTechWriter]

No description provided.

[Copilot]

Pull Request Overview

This PR updates the documentation for the Diffbot extension in the README.md file. The changes improve clarity, correct grammatical errors and typos, and add important information about subscription requirements.

Key Changes:

• Added a warning section about DiffBot subscription requirements and data processing
• Fixed several grammatical errors and typos throughout the documentation
• Improved phrasing for better readability

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[dlavrenuek]

Chank you for the improvements @CognigyTechWriter. Based on how I understood the task also the description that is displayed to users in the marketplace/installed extensions should make it explicit that a Diffbot account is needed. This is done here and here (but this one requires creating a new release of diffbot extension and I will also need to copy the changes to a different repository)