Clarify timeout option in Readme

worker.Immediately has value 2 which means the job will timeout after 2 seconds (maybe not very intuitive?). To have no timeout one has to pass the value 0 which is also constant worker.Unlimited (more intuitive)
Merge pull request #29 from sgrimee/patch-2

Clarify timeout option in Readme
SUBMIT_JOB_SCHED is deprecated, worker.Immediately should be removed.