Add alternative sacct call and notes to slurm_acc
Add alternative sacct call and notes to slurm_acc

- Provide alternative calls to sacct so users can decide how they report
their CPU duration.
- Comments added to explain overall script and these choices.

apel/apel,apel/apel,stfc/apel,stfc/apel,tofu-rocketry/apel,tofu-rocketry/apel