chore: import upstream snapshot with attribution

packages/plugins/threads/README.md

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+# @docmd/plugin-threads
+
+Adds inline discussion threads to your docmd site - stored directly in Markdown as `::: threads` containers, so comments live in your repo and sync with your Git and PR workflows. Supports text highlighting, replies, thread resolution, and emoji reactions. An optional plugin, installed separately.
+
+```bash
+docmd add threads
+```
+
+Original author: [@svallory](https://github.com/svallory)
+
+Part of the **[docmd](https://github.com/docmd-io/docmd)** documentation engine.
+
+## Documentation
+
+See **[docs.docmd.io](https://docs.docmd.io)** for full usage and API reference.
+
+## License
+
+MIT