Added example for using module purge
also added a few more examples in a new section Troubleshooting.

Added brief examples at the beginning
separated private and project modules
Added content where there was a todo

together with Martin, thank you for helping me with this.

(zu lange Zeilen, fehlende Zeilenumbrüche, "filesystems" klein geschrieben)

(zu lange Zeilen, fehlende Zeilenumbrüche, "filesystems" klein geschrieben)

I re-styled most of modules.md to befit our contribution guidelines,
and furthermore rewrote part of it to make it more readily understandable
to *Bob Weatherscientist*.

I re-styled most of modules.md to befit our contribution guidelines,
and furthermore rewrote part of it to make it more readily understandable
to *Bob Weatherscientist*.

* Restructure