Installtion Of Asset Plugin Error

I m trying to install yii 2.0 basic app installation on windows

i give the following command to the composer as written in the documentation of the yii 2

composer global require "fxp/composer-asset-plugin:1.0.0-beta2"

but i got the follwing error message

The requested package "fxp/composer-asset-plugin:1.0.0-beta2" could not be found in any version,there may be a typo in the package name. The error message image is also attached please see and help me.

Try adding --dev.