[DOC] retrieve submodules at clone in guide

The git clone command was missing the automatic retrieve of submodules.

Issue-ID: DOC-618
Signed-off-by: Sylvain Desbureaux <sylvain.desbureaux@orange.com>
Change-Id: Ic43fa71c3b931b21160095ed9a9f4e48f733cbf4
1 file changed