docs(Build Cop): expand README, document flags (#320)
docs(Build Cop): expand README, document flags (#320)

Co-authored-by: Justin Beckwith <0b357449eb5b1ce3bad523b6be0681e856776d8e@gmail.com>

googleapis/repo-automation-bots,googleapis/repo-automation-bots,googleapis/repo-automation-bots,googleapis/repo-automation-bots,googleapis/repo-automation-bots