chore(java): add a note in README for migrated split repos (#1687)#1392

gcf-merge-on-green[bot] merged 1 commit intomaingoogleapis/java-pubsub:mainfrom

owl-bot-update-lock-edae91ccdd2dded2f572ec341a768ad180305a3e8fbfd93064b28e237d35920agoogleapis/java-pubsub:owl-bot-update-lock-edae91ccdd2dded2f572ec341a768ad180305a3e8fbfd93064b28e237d35920aCopy head branch name to clipboard