Remove gist link that (never?) doesn't work

Summary: Removing 404 link, fixes https://github.com/phacility/arcanist/issues/180

Test Plan: n/a

Reviewers: epriestley, avivey

Reviewed By: epriestley, avivey

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D10689
Merge branch 'master' of github.com:facebook/arcanist