Update README.md

Added a server template in the documentation for Debian 7 / Ubuntu 14.04 / CentOS 6.5 / CentOS 7 and Amazon Linux. This allows users to:
 - Have working instructions to install the application from scratch 
 - Create a temporarily server with a working version of tutanota to play around
 - Deploy a production server with tutanota

I think this is a great add-on for the documentation. Novice users will be able to run the application with no problem and advanced users has templates that they just need to customise.

Feedback is appreciated!
Merge pull request #4 from tk421/master

Update README.md