Add guidelines for Visual Studio extension development using Communit…

[madskristensen]

…y.VisualStudio.Toolkit

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• My contribution adds a new instruction, prompt, or chat mode file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, or chat mode with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.

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Description

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Type of Contribution

• New instruction file.
• New prompt file.
• New chat mode file.
• New collection file.
• Update to existing instruction, prompt, chat mode, or collection.
• Other (please specify):

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Additional Notes

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By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.

[Copilot]

Pull request overview

This pull request adds comprehensive guidelines for Visual Studio extension development using the Community.VisualStudio.Toolkit. The contribution provides detailed instructions to help GitHub Copilot assist developers in building VSIX extensions following best practices for threading, theming, and the VS SDK.

• New instruction file for Community.VisualStudio.Toolkit-based VSIX development
• README.md updated with proper entry and installation badges

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
instructions/vsixtoolkit.instructions.md	Comprehensive 647-line instruction file covering VSIX development patterns, threading guidelines, theming, VS SDK APIs, MEF components, best practices, and marketplace presentation guidelines
docs/README.instructions.md	Added entry for the new instruction file with proper formatting and installation links for VS Code and VS Code Insiders

The new instruction file is well-structured with:

• Proper markdown front matter with description and applyTo fields
• Clear scope definition specifying when to apply these instructions
• Comprehensive coverage of toolkit patterns (BaseCommand, ToolkitPackage, BaseOptionModel)
• Threading guidelines with VSTHRD analyzer rules
• Visual Studio theming guidance
• Common pitfalls and solutions
• README and marketplace presentation best practices

The file follows the established conventions for instruction files in this repository, uses lowercase hyphenated naming (vsixtoolkit.instructions.md), and includes all required front matter fields with properly quoted values.