A proof-of-concept plugin sharing site is available at codedraken.github.io/ES-Mod-Share.
Instructions for creating plugins are on the wiki.
Eventually, it will be possible to download and install plugins from within the game. To support both that and a more detailed plugin listing here on the website, each plugin will need to provide, at minimum:
A title, author name, and short description.
A longer description to be shown if the user clicks on a particular plugin in the gallery to view more information.
A list of tags to be used when filtering the plugin list.
A "cover image" representing the mod. These will all be required to be a certain size, but I haven't decided yet what the size should be.
One or more screenshots of the plugin in action. All screenshots should have a 16:9 aspect ratio, e.g. 1280×720 or 1920×1080. (You can edit your preferences file to set the window size to an exact value.)
A download link to a zip file. Ideally, the download link changes every time a new version of the mod is released, both so that older versions remain accessible and so that the game client will be able to tell from the path when a new version is available.
The preferred way to host a plugin is to create a GitHub repository for it. The "gh-pages" branch of the repository should contain the cover image and screenshots, and may also host a web page providing more information about the plugin. The "master" branch should contain the plugin itself. New downloads can be created just by tagging a release in the master branch.