[FEATURE:jobs/gnu-parallel] Add a new page with instructions for launching GNU parallel

[codeharris]

No description provided.

[codeharris]

• Decide which features from the tutorials should be included in the documentation
• Not all scripts were tested

[jhale]

Small comment here on a quick scan - you should explicitly explain how srun within an outer sbatch works and what it does, it's a bit magic.

[gkaf89]

Small comment here on a quick scan - you should explicitly explain how srun within an outer sbatch works and what it does, it's a bit magic.

@jhale We are preparing a page about job steps, it's just not public yet!