Update index.md

Hey Guys,
i'm using Cordova a long time and therefore i read the documentation. My english is not as i good as that from my english teacher was. But my german is nearly perfect. So i took your GER-index.md and translated the first Plugin here into German. In the next Weeks/Month i would like to translate the other Plugins into German. This is my first work on Github and i hope, you accept my edit. 

If you have questions or something like that, you can write me an e-mail to: sit@posteo.de 

Hope to hear from you soon,
best regards from germany,
Christopher