docs: Update README with new accelerators and playbook links

[Prajwal-Microsoft]

Added new sections for Document Processing Accelerator and GPT-RAG Accelerator, along with links and descriptions. Updated playbook information for AI and Data Engineering.

Purpose

This pull request updates the README.md file to enhance the list of related solution accelerators and introduce new resources for best practices. The main changes include adding new solution accelerator links and a new section highlighting Microsoft's AI and Data Engineering playbooks.

Additions to solution accelerators:

• Added the Document Processing Accelerator and GPT-RAG Accelerator to the "Check out similar solution accelerators" section, providing more options for modular document processing and secure enterprise GPT assistant frameworks.

New best practices resources:

• Introduced a new section with links to Microsoft's AI and Data Engineering playbooks, offering guidance and code samples for real-world enterprise AI and data engineering problems.

Does this introduce a breaking change?

• Yes
• No

Golden Path Validation

• I have tested the primary workflows (the "golden path") to ensure they function correctly without errors.

Deployment Validation

• I have validated the deployment process successfully and all services are running as expected with this change.

What to Check

Verify that the following are valid

• ...

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