Explain reasoning behind kitty gifts

Summary: I find this fact very useful for understanding my feline companion

Test Plan: Added "Motivator: Cat Facts" to the project, nothing broke

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D16374