Make repo "executable" via Nextflow

[julianu]

As Nextflow has the option to directly "execute" repos on GitHub, we should re-structure it to make this possible. I don't know, whether this is much work or works out of the box for us, but would make things for new users much easier.

My idea would be to allow direct execution as shown here: https://www.nextflow.io/docs/latest/sharing.html
nextflow run mpc-bioinformatics/McQuaC