that message is expected as there is no configuration provided for the plug-in from that part of the preferences. and having never used the webdev plug-in, i don't know what config options it provides though i'd suspect it's somewhere in the view provided in the library tree.
Yea i found out that... now you can create it from the webdev plugin interface ... but the thing is that wiki needs to be updated
How did you do that? If I click on the "WebDev Platform" entry in media library there is only a message "Please select a device or a subitem of a device.". But it's the same message clicking on subitems "Online Documentation" or "JSAPI2 Test"