few more docs

Hi,

although I might touch these sources again tomorrow, I thought it's good to open a PR in order to receive early feedback (mostly of crude type about missing pieces/paragraphs). Yet, any feedback is welcome :)

tia, F.
on 2nd thought, using an option with a `-` in the name is actually good, since it shows how the `-` is handled on the various levels

so, use `--foo-bar` instead, and use `baz` as a value?

or even better, use a concrete example with a `-` in it, e.g. `--modules-tool` (with `Lmod` as a value)