Docs: add Go to the main README

[Quim Muntal (qmuntal)]

Motivation & Context

The repository includes a Go directory, while the Go SDK is developed and supported in a separate repository. A clear cross-reference prevents users from looking for Go documentation, samples, contribution guidance, or issue tracking in the Python/.NET repository.

Description & Review Guide

• What are the major changes? Adds a single explicit Go SDK cross-reference to the main README and a small go/README.md redirect to the dedicated Go repository.
• What is the impact of these changes? Documentation-only. The main README remains focused on Python and .NET while clearly directing Go users to the correct repository.
• What do you want reviewers to focus on? Verify that the wording clearly separates repository ownership and routes Go users to the dedicated repository.

Related Issue

Fixes#7753

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.

[Copilot]

Pull request overview

Adds public-preview Go SDK discovery and onboarding to the main documentation.

Changes:

• Adds Go links, installation, quickstart, features, and samples.
• Adds a local Go README redirecting to the dedicated repository.
• Updates the README navigation and environment guidance.

Show a summary per file

File	Description
README.md	Integrates Go throughout the main documentation.
go/README.md	Redirects Go users to the dedicated repository.

Review details

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• Files reviewed: 2/2 changed files
• Comments generated: 3
• Review effort level: Balanced