Added FAQ: How do I shut down ``celeryd`` safely?
Added FAQ: How do I shut down ``celeryd`` safely?

cbrepo/celery,frac/celery,WoLpH/celery,mitsuhiko/celery,frac/celery,WoLpH/celery,ask/celery,ask/celery,cbrepo/celery,mitsuhiko/celery