doc quantum_region_name option

fixes bug 1111109

Grizzly introduced a new option: quantum_region_name which is
important for multi-region. This patch adds the option to the
reference.

There were no examples that I could find in the docs that
would need to be updated for the use of this option.

Change-Id: Ia2d111f7f475a748ca6c717c53d6f79d4ab05496