Rewrite/improve Emma top level documentation

[holzkohlengrill]

Feature Description

In order get a more gentle introduction and better presentation of Emma a rework of the top level (README.md) readme would be beneficial.

• Some parts are too technical and should be moved to the in-depth/formal documentation part of Emma
• The introduction is to hard to read and some text passages are too long

Our recent email to the GENIVI projects mailing list could be a good starting point.