The discovery rules page is a part of the host discovery guide and will only exist if this plugin is installed on your orcharhino.
The discovery rules page can be accessed via the configure menu:
Configure > Discovery rules
The discovery rules page exists to list any discovery rules. Such rules can be used to provision a set of hosts that have similar facts with the same configuration. In particular, they allow for the automatic assignment of discovered hosts to a host group and a context. They also allow the hostname to be set dynamically using the eRuby-template language.