Update the luancher example page

[codeharris]

The Slurm launcher example page is out of date.

1. Update the availability of [Iris nodes](See the Link: https://hpc-docs.uni.lu/slurm/launchers/#resource-allocation-guidelines). For instance, many Skylake nodes have moved to the Grid'5000 partition and the Hopper node does not appear.
2. Format all Slurm launcher scripts so that they use long form options in the SBATCH directives.
3. The section on embarrassingly parallel jobs is too wordy. For the documentation an explanation of what an embarrassingly parallel job is suffices. Probably this section should be moved to a new page that links to Arrays and GNU parallel.