MultiQC and Documentation Improvements

[jfy133]

This includes the following:

• Slight modification to MPI-SHH profile while we wait for singularity to be fixed
• Addition to documentation specifying how to specify a software environment cache (related to above - we have limited home directories so needed to specify another location)
• Made a working MultiQC config after Alex identified the issue ;)

Note: Note sure the changelog system - @apeltzer please update it accordingly, and you can explain to me how you want it to function in the future.

PR checklist

• This comment contains a description of changes (with reason)

Learn more about contributing: https://github.com/nf-core/eager/tree/master/.github/CONTRIBUTING.md

[apeltzer]

Maybe incorporate here a URL for caching singularity images?

cacheDir = "/projects1/users/$USER/nextflow/nf_cache/singularity/"

[apeltzer]

Hm, no. We need to have different profiles then for Jena if you guys want to have both .... or you need to specify this in a different profile - I personally would love to keep using Singularity as this is more stable.