Add Petrel & OSTC3 support to the list of updates

This has been requested several places, so let's just put it in
plain view for everyone

Signed-off-by: Henrik Brautaset Aronsen <subsurface@henrik.synth.no>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Hardware updates for README, ReleaseNotes.txt and user-manual

Decided to split OSTC3 and Petrel in the ReleaseNotes (as the Petrel was
already supported in 3.0) and added the Suunto DX as well.

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