Add Travis to Readme

tells people, how to find the CI server.

For further details read Issue #22.

Signed-off-by: Erik Bernoth <bernoth@dresearch-fe.de>
Acked-by: Steffen Sledz <sledz@dresearch-fe.de>
Acked-by: Eik Binschek <binschek@dresearch-fe.de>
Merge branch 'f-add-travis-to-readme-v2' into dev

close #22