Directory containing optional site configuration files. To use, rename this
directory from "etc/opt.example/" to "etc/opt/". Add optional configuration
files with names such as "rose-key1.conf", "rose-key2.conf", etc. In
"etc/rose.conf", add "opts=key1 key2" to switch on the optional configurations.

See
http://metomi.github.io/rose/doc/html/api/configuration/rose-configuration-format.html#optional-configuration
for information on optional configurations.
