More SVN hook docs.
More SVN hook docs.

Summary:

Test Plan:

Reviewers:

CC:

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