ansible dependencies are not automatically downloaded on production deploy

[paolantoni]

The how to is unclear about the ansible dependencies management.
Following the guide the user see this error:
ERROR! the role 'azavea.python-security' was not found in ....

Please consider to improve the how to with the command:
ansible-galaxy install -r deployment/ansible/roles.yml --roles-path deployment/ansible/roles
that fixes the error about missing dependencies.