Add a specific documentation about the process to be done about the
number version for Maven release versus the Eclipse release.

An exchange about this subject is in progress in HelpDesk#6329 [1]. The
documentation and the described approach could be changed according to
the decision that will be taken in the future.

[1] eclipsefdn/helpdesk#6329



Signed-off-by: Laurent Redor <laurent.redor@obeo.fr>