[PD-899] Add help text to job view

This addresses the issue of notifying a user that there could be a delay between when the job link appears and when a job is actually available at that link. 

I moved the early bail out for the template tag so that we aren't needlessly doing queries on a job that hasn't even been approved. 

The issue of how best to represent job links has been deferred to a separate ticket (linked to in pd-899).