Add comprehensive documentation for PR approval policy and repository contribution guidelines

[Copilot]

This PR addresses the question "what is the correct method to approve a PR?" by adding comprehensive documentation that clarifies the repository's pull request policy and provides guidance for contributors.

Changes Made

1. Created PR_APPROVAL_POLICY.md

Added a detailed policy document that explains:

• Repository PR Policy: This repository does not accept pull requests as it contains read-only sample code for Dragon Medical SpeechKit .NET SDK
• Support Channels: Clear guidance on where to get help with Dragon Medical SpeechKit
• Application Document Approval: Documentation of the internal document approval workflow found in the codebase, including DocumentStates enum usage and examples from the existing code

2. Enhanced CONTRIBUTING.md

Restructured the contribution guidelines with:

• Clear warning about no pull requests being accepted
• Better organization with proper headings and sections
• Reference to the new PR policy document
• Guidance on reporting issues through proper channels

3. Updated README.md

Added prominent notice in the main README that:

• Immediately informs users that PRs are not accepted
• References the detailed PR policy documentation
• Maintains all existing documentation links

Context

The repository contains sample code for Dragon Medical SpeechKit .NET SDK integration. The codebase includes document approval workflows (using DocumentStates.Corrected, DocumentStates.Uncorrected, etc.) which could be confused with GitHub PR approval processes. This documentation clearly separates the two concepts and provides appropriate guidance for each.

Impact

• For Contributors: Clear understanding that this is a read-only repository with no PR acceptance
• For Support: Proper channels are now clearly documented
• For Integration: Document approval workflow examples are properly documented for developers integrating with the SDK

The changes maintain the repository's purpose as a reference while eliminating confusion about contribution processes.

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