[docs] Add phase about release candidate version.
[docs] Add phase about release candidate version.

Signed-off-by: Stéphane Galland <23860b554af9116d4237121086bd6767cdd4ff4b@arakhne.org>

jgfoster/sarl,sarl/sarl,sarl/sarl,gallandarakhneorg/sarl,sarl/sarl,sarl/sarl,sarl/sarl,jgfoster/sarl,gallandarakhneorg/sarl,jgfoster/sarl,jgfoster/sarl,gallandarakhneorg/sarl,sarl/sarl