At the point when the developer mode is introduced in the training, it is
confusing because the documentation page describes the option inside the
Settings page, but that page only appears if at least one application is
installed. (Otherwise, the Settings app shows the Users instead)
This commit adds a note so that the reader does not start looking for a
screen that cannot be reached at that point.
task-2822582
X-original-commit: 2ebb7fe802
Part-of: odoo/documentation#1828
0a3dd86eef