component-guide: update `adding new packages from debian` section

Add a note about project visibility when creating an empty project. If the project visibility is not Public, gitlab-rulez will fail with the below error,

$ ./gitlab-rulez apply rulez.yaml --filter pkg/linuxptp
-----------[ cut here ]------------
found 1 errors
project pkg/linuxptp: settings: save changes -> error: 403: 403 Forbidden

Signed-off-by: Vignesh Raman vignesh.raman@collabora.com