Add documentation writer prompt

[geoder101]

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 node update-readme.js and verified that README.md is up to date.

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Description

Adds a new prompt which turns the agent into an expert technical writer specializing in creating high-quality software documentation, guided by the principles and structure of the Diátaxis technical documentation authoring framework (see: https://diataxis.fr/)

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Type of Contribution

• New instruction file.
• New prompt file.
• New chat mode file.
• Other (please specify):

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Additional Notes

Here are some screenshots of a small example:

Mind that the prompt file was initially named "documentation-expert.prompt.md", but then I renamed it to "documentation-writer.prompt.md" (right before opening this PR)

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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 PR adds a new prompt file that creates a documentation writing assistant based on the Diátaxis framework, designed to help developers create structured, high-quality technical documentation.

• Introduces a documentation expert prompt that follows the Diátaxis methodology for creating tutorials, how-to guides, reference materials, and explanations
• Implements a structured workflow that ensures proper document planning and user needs assessment before content creation
• Updates the README to include the new prompt in the available templates list

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
prompts/documentation-writer.prompt.md	New prompt file implementing a Diátaxis-based documentation writing assistant with structured workflow and clear principles
README.md	Added entry for the new documentation writer prompt in the prompts table