Craft 3 doesn't see my Commerce plugin I am running a local install of Craft 3 Pro dev preview using MAMP and Sequel Pro on my iMac.  I downloaded the Commerce plugin to try it out and dropped the 'commerce' folder into my craft/plugins folder.  When I visit the admin control panel and click on plugins, I can't see the Commerce folder/plugin I just added. Any suggestions as to why?
The whole plugin API has gotten an overhaul in Craft 3, so all plugins needs to be rewritten/updated to work with Craft 3. 

Craft Commerce hasn't been updated yet. If it had there would be separate versions for Craft 2 and 3 for download.