This patch adds a document which is supposed to help tempest
contributors to start with tobiko.
The doc mentions some big differences between tempest and tobiko.
In order to see the changed docs, please access:
Zull run -> openstack-tox-docs -> Logs tab -> docs (raw).
Change-Id: Ie757041d49199213641b347f898ea97f72c96fce
b785dee6c1