Updated openstack/openstack
Project: openstack/oslo.config  f18797ab7d068663b37f4e25558c624f44e4b099

Add warning about interpolating values from groups

Add a warning explaining that options in groups cannot be used with
the interpolation syntax.

Reformat note to use directive so it is highlighted.

Add "docs" section to tox.ini to make testing doc build easier.

Change-Id: If5106aa44d4c87abe84a7fb7a250541bba9f5068