[TASK] Improve visibility of composer notice in install documentation

[TASK] Improve visibility of composer notice in install documentation

The notice about running composer install --no-dev is hidden from view.

Move it to the front into an own box to have the same visibility
for all commands that need execution.

Resolves: #72651
Releases: master,7.6
Change-Id: I530a754c319e31285701e1af83ab475aeb59ede6
Reviewed-on: https://review.typo3.org/45829
Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Tested-by: Mathias Brodala <mbrodala@pagemachine.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Peter Foerger <pfoerger@mac.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>