Fix Orleans.Serialization.Protobuf README to document Google.Protobuf instead of protobuf-net

[Copilot]

• Review the current README and identify incorrect information
• Update the README to show Google.Protobuf usage instead of protobuf-net
• Update example code to demonstrate .proto file usage
• Update example code to show proper Google.Protobuf attributes and patterns
• Verify the documentation is consistent with the actual implementation
• Build the project to ensure no issues
• Streamline README by referencing Microsoft's official Protobuf documentation
• Complete the task

Summary

Updated the README to be more concise and reference Microsoft's official documentation:

Changes:

• Made introduction more concise
• Replaced detailed .proto file and project configuration instructions with reference to Create Protobuf messages for .NET apps
• Simplified example code, removing redundant explanations
• Consolidated collections section into a brief note
• Added official Microsoft Protobuf guide to documentation section
• Removed generic Protocol Buffers documentation link in favor of .NET-specific guidance

This follows the feedback to "ground the document by reading the Microsoft documentation and incorporating it" while removing unnecessary details that are already covered in the official guide.

Original prompt

On Orleans.Serialization.Protobuf, Fix this README to align with reality - for example, note that this adds support for Google.Protobuf, but the README currently shows attributes for a different package.

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Microsoft Reviewers: Open in CodeFlow

[ReubenBond]

@copilot Ground the document by reading https://learn.microsoft.com/en-us/aspnet/core/grpc/protobuf?view=aspnetcore-9.0 and incorporating it. Ideally, reference it so that we can remove unnecessary details

[Copilot]

@copilot Ground the document by reading https://learn.microsoft.com/en-us/aspnet/core/grpc/protobuf?view=aspnetcore-9.0 and incorporating it. Ideally, reference it so that we can remove unnecessary de...

Done. The README now references the Microsoft documentation and removes the detailed setup instructions that are covered there. See commit 4360f06.

[Copilot]

Pull Request Overview

This PR updates the Orleans.Serialization.Protobuf README to correctly document Google.Protobuf integration instead of protobuf-net, which was incorrectly referenced in the original documentation.

Key changes:

• Updated introduction to explicitly mention Google.Protobuf package
• Streamlined documentation by referencing Microsoft's official Protobuf guide instead of duplicating setup instructions
• Simplified example code and removed protobuf-net specific attributes