This website is a simple HTML static webpage.
Update the files plugins.json and index.html, then send a pull-request.
compatible_versionis the latest stable version tested with your plugin.remote_installallows people to install the plugin from the Kanboard user interface.
Your plugin archive must contains a folder with the plugin name (namespace), example:
MyPlugin-1.0.0.zip
└── MyPlugin
├── Controller
├── Locale
│ └── fr_FR
├── Template
│ ├── ...
├── Test
│ └── ...
└── ...
The archive will be extracted by Kanboard into the folder plugins as plugins/MyPlugin.