Add contribution guidelines.
Merge branch 'master' of github.com:susestudio/studio-help

* 'master' of github.com:susestudio/studio-help:
  BNC#827779 Remove /help/create/howto/hyperv.html stub
  Fixed bnc#808381 and added missing types to API documentation
  Small additions for bnc#808377
  Fixed bnc#808377 and added a brief description about qcow2