Say until when the reviewers are away
Say until when the reviewers are away

Test Plan: `arc diff` with reviewers away.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D2496

calblueprint/arcanist,wxstars/arcanist,sneakpeeq/arcanist,wxstars/arcanist,fivestars/arcanist,memsql/arcanist,sneakpeeq/arcanist,jra3/arcanist,chundongwang/arcanist,eSpark/arcanist,uber/arcanist,r4nt/arcanist,codelabs-ch/arcanist,eSpark/arcanist,r4nt/arcanist,Symplicity/arcanist,wxstars/arcanist,KieranHayes/arcanist,fivestars/arcanist,codelabs-ch/arcanist,hach-que/arcanist,codelabs-ch/arcanist,folsom-labs/arcanist,haskell-infra/arcanist,codelabs-ch/arcanist,julkiewicz/arcanist,aik099/arcanist,wharris/arcanist,uber/arcanist,PageUpPeopleOrg/arcanist-patches,r4nt/arcanist,zhihu/arcanist,hach-que/arcanist,julkiewicz/arcanist,wikimedia/phabricator-arcanist,julkiewicz/arcanist,dguo-coursera/arcanist,dguo-coursera/arcanist,wharris/arcanist,KieranHayes/arcanist,zhihu/arcanist,uber/arcanist,aik099/arcanist,alexmv/arcanist,Symplicity/arcanist,sneakpeeq/arcanist,alexmv/arcanist,jra3/arcanist,wharris/arcanist,zhihu/arcanist,Khan/arcanist,wikimedia/phabricator-arcanist,calblueprint/arcanist,KieranHayes/arcanist,memsql/arcanist,haskell-infra/arcanist,folsom-labs/arcanist,folsom-labs/arcanist,jra3/arcanist,eSpark/arcanist,eSpark/arcanist,folsom-labs/arcanist,phacility/arcanist,calblueprint/arcanist,memsql/arcanist,coursera/arcanist,jra3/arcanist,haskell-infra/arcanist,haskell-infra/arcanist,dguo-coursera/arcanist,fivestars/arcanist,sneakpeeq/arcanist,aik099/arcanist,PageUpPeopleOrg/arcanist-patches,hach-que/arcanist,julkiewicz/arcanist,wikimedia/phabricator-arcanist,hach-que/arcanist,kevinseelbach/arcanist,coursera/arcanist,r4nt/arcanist,chundongwang/arcanist,chundongwang/arcanist,fivestars/arcanist,kevinseelbach/arcanist,PageUpPeopleOrg/arcanist-patches,dguo-coursera/arcanist,coursera/arcanist,phacility/arcanist,phacility/arcanist,phacility/arcanist,alexmv/arcanist,memsql/arcanist,wikimedia/phabricator-arcanist,PageUpPeopleOrg/arcanist-patches,Symplicity/arcanist,chundongwang/arcanist,Khan/arcanist,phacility/arcanist,Symplicity/arcanist,KieranHayes/arcanist,Khan/arcanist,codelabs-ch/arcanist,kevinseelbach/arcanist,alexmv/arcanist,wharris/arcanist,kevinseelbach/arcanist,wxstars/arcanist,uber/arcanist,zhihu/arcanist,aik099/arcanist,coursera/arcanist,calblueprint/arcanist,Khan/arcanist