Update start/stop API docs: Windows does take over threads
Update start/stop API docs: Windows does take over threads

The docs had a stale comment about Windows not taking over threads when
dr_app_start() was invoked.

Review-URL: https://codereview.appspot.com/309250043

AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio