Remove Google analytics

[Bananeweizen]

docs/index.html contains Google Analytics. If people use that file to start their own radar, they may miss the necessity to remove that script. Therefore it might be a good idea to remove it entirely from that demo document.

[hjacobs]

I guess we won't remove the GA code as we are using it for our tracking (docs/index.html is the source of https://opensource.zalando.com/tech-radar/), but it absolutely makes sense to highlight this in the README and the HTML itself, so people don't forget to change it or remove it.