User manual: Give credit where it's due

Willem has been maintaining the user manual for quite a while and at this
point is the main author, so he should be listed first.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
User manual: gps coordinates are tied to location names

While it seems obvious that you need a named dive site in order to track
its coordinates, apparently people try to have no location name but
distinct coordinates which at this time we do not support.

See #440

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
User manual: update html file

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>