With both the installer and package downloaded from github i was getting:
>» Installing Cocos2D-v3.0.0 files
>» Installing Cocos2D-v3.0.0 templates
>» Building/Installing Cocos2D-v3.0.0 documentation, this may take a minute….
appledoc version: 2.2 (build 963)
Generation step 1/5 failed: GBHTMLOutputGenerator failed copying template files to output, aborting!
You don’t have permission to save the file “api-docs”.
You don’t have permission.
>» Cocos2D-v3.0.0 installation complete!
It seams that the user which you are using to install Cocos 2d has to belong to the sudoers file.
Check Google for more details on how to do this.