Added Notice-Information in README.md, because when downloading the app ...

...from the ownloud repository, it won't work at first. see: http://doc.owncloud.org/server/7.0/developer_manual/app/app/info.html

and: http://stackoverflow.com/questions/21700112/no-app-name-specified-in-owncloud

Maybe a even better solution is to provide a proper download-link in the owncloud repository, which provides the correct folder-name.