Fix Executor doc
Fix Executor doc

To use a Future with a custom ThreadPoolExecutor you have to pass it in
to Future.execute

MadBomber/concurrent-ruby,lucasallan/concurrent-ruby,hobodave/concurrent-ruby,hobodave/concurrent-ruby,lucasallan/concurrent-ruby,MadBomber/concurrent-ruby,MadBomber/concurrent-ruby,lucasallan/concurrent-ruby,lucasallan/concurrent-ruby,MadBomber/concurrent-ruby,hobodave/concurrent-ruby,lucasallan/concurrent-ruby,hobodave/concurrent-ruby