"No archetype repository found" when generating project following instruction in howto "Start a project"

As reported by Danilo Ardicilii (see http://n2.nabble.com/Hippo-Site-Toolkit-2---Start-a-project-td2297035.html#a2297035):

Hi,
there is a problem in the Hippo Site Toolkit 2 guide ( Hippo Site Toolkit 2 - Start a project: http://www.onehippo.org/site-toolkit/delve_into/howto/start_project.html ).
I used the command "mvn archetype:generate ..." and maven tries to reach the maven's repository and this involves the following warnings:
"[WARNING] No archetype repository found. Falling back to central repository (http://repo1.maven.org/maven2).
[WARNING] Use -DarchetypeRepository=<your repository> if archetype's repository is elsewhere."
I solved this problem appending the attribute "-DarchetypeRepository=http://repository.hippocms.org/maven2" at the "mvn archetype:generate" command.

Danilo