R1:16a7eaa70044

Fix wrong link to "Create Rule" in Herald mobile view

Summary: The link pointed to `create/`, which gives as `404`.

Test Plan: clicked the link. It worked.

Reviewers: epriestley, #blessed_reviewers, chad

Reviewed By: chad

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D7698