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.
use `$EASYBUILD_INSTALLPATH` (note the `_`, without it you're using old-style configuration which is going to break in EasyBuild v2.0).