A further update to the user manual

I have added a section about importing dives from other electronic
sources. There are some potential problems, because I know that the
intercation with divelogs.de is not yet fully functional

Signed-off-by: Willem Ferguson <willemferguson@zoology.up.ac.za>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>