Add docmd to Documentation

[mgks]

Description

Adds docmd to the Documentation category.

Why docmd should be included

docmd is a zero-configuration tool that generates static documentation sites from Markdown. It distinguishes itself with built-in offline search and custom containers, offering a simpler alternative to React-based generators.

It meets the requirements:

• Repo is >30 days old (6 months).
• Repo has >100 stars (500+ stars).
• Tested and documented.

Placement

Added alphabetically between Docco and documentation.js in the "Documentation" section.

By submitting this pull request, I promise I have read the contribution guidelines twice and ensured my submission follows it. I realize not doing so wastes the maintainers' time that they could have spent making the world better. 🖖

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