Add plugin submission guide for the marketplace

New wiki page documenting how to get a plugin listed (PR adding a
descriptor to various.json, source/format/value requirements), linked
from the nav and Start page. CONTRIBUTING.md points GitHub submitters
to it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: undera

CONTRIBUTING.md

@@ -0,0 +1,8 @@
+# Contributing
+
+**Listing your plugin in the marketplace** — see
+[Submitting Your Plugin to the Marketplace](https://jmeter-plugins.org/wiki/SubmitYourPlugin/).
+In short: open a PR adding a descriptor entry to `site/dat/repo/various.json`.
+
+**Contributing plugin code to this project** — see the
+[Developers Guidelines](https://jmeter-plugins.org/wiki/DeveloperGuide/).

site/dat/wiki/Start.md

@@ -90,6 +90,7 @@
 # Developing Plugins
   - [Contibutors List](/wiki/Contributors/) - write down yourself, if you took your part
   - [DeveloperGuide](/wiki/DeveloperGuide/)
+  - [Submitting Your Plugin to the Marketplace](/wiki/SubmitYourPlugin/)
   - [BuildingFromSource](/wiki/BuildingFromSource/)
   - [PluginsGuiGuidelines](/wiki/PluginsGuiGuidelines/)
   - [Roadmap](/wiki/Roadmap/) and [Changelog](/wiki/Changelog/)

site/dat/wiki/SubmitYourPlugin.md

@@ -0,0 +1,32 @@
+# Submitting Your Plugin to the Marketplace
+
+If you have published a JMeter plugin and want it listed in the
+[Plugins Manager](/wiki/PluginsManager/) catalogue, send a pull request to the
+[project repository](https://github.com/undera/jmeter-plugins). You add a small descriptor
+that points at your released artifact — the plugin code itself stays in your own repository.
+
+## What to change
+
+- **New plugin:** append one entry to `site/dat/repo/various.json` (the array of community
+  plugins). Do not create a new `.json` file.
+- **New version of a plugin already listed:** add a key to that plugin's existing `versions`
+  map.
+
+For the full list of descriptor fields and a complete example, see
+[Plugin Repository Descriptor Format](/wiki/PluginRepositoryDescriptorFormat/).
+
+## Requirements
+
+- **Stable download location.** Each version's `downloadUrl` must point at
+  [Maven Central](https://central.sonatype.com/) or your project's GitHub releases — a public,
+  permanent URL.
+- **Version key matches the artifact.** The key in the `versions` map must match the version in
+  the JAR filename, e.g. `1.0.4` ↔ `…/my-plugin-1.0.4.jar`.
+- **Formatting.** Run `python3 format_repo.py` before committing. CI verifies this with
+  `python3 format_repo.py --check`; the JSON must use 2-space indentation and end with a
+  newline.
+- **Real, reusable value.** The plugin should do something not already covered by a built-in
+  JMeter feature or a plugin already in the catalogue.
+
+Contributing plugin *code* to this project (rather than listing your own) is covered by the
+[Developers Guidelines](/wiki/DeveloperGuide/).

site/mkdocs.yml

@@ -108,6 +108,7 @@ nav:
       - wiki/BuildingFromSource.md
       - wiki/PluginsGuiGuidelines.md
       - wiki/PluginRepositoryDescriptorFormat.md
+      - wiki/SubmitYourPlugin.md
       - wiki/Contributors.md
       - wiki/Roadmap.md
       - wiki/Changelog.md