Add prefix and reverse notation to schema
Add prefix and reverse notation to schema

Summary:
This changes updates the schema docs to include mention of the
implicit /kythe prefix and % notation for reversed edges.

Test Plan: it builds

Reviewers: schroederc, zarko

Reviewed By: zarko

Subscribers: jrtom, #core_team

Differential Revision: https://phabricator-dot-kythe-repo.appspot.com/D1924

bzz/kythe,kythe/kythe,bzz/kythe,benjyw/kythe,benjyw/kythe,kythe/kythe,benjyw/kythe,kythe/kythe,bzz/kythe,benjyw/kythe,benjyw/kythe,kythe/kythe,benjyw/kythe,benjyw/kythe,benjyw/kythe,bzz/kythe,benjyw/kythe,bzz/kythe,bzz/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,bzz/kythe,bzz/kythe,bzz/kythe,kythe/kythe,benjyw/kythe,kythe/kythe,bzz/kythe,bzz/kythe,kythe/kythe,bzz/kythe,benjyw/kythe,benjyw/kythe