To share your dev plugin as a zip archive, you simply select Download this plugin from the actions menu of the plugin. Alternatively you can compress the contents of the plugin folder to a Zip file (the contents of the plugin folder must be at the root of the Zip file, i.e. there must not be any leading folder in the Zip file). The plugin.json file should be at the root of the Zip file.
A typical Zip file would therefore have this structure