manual: Add singular example for dependency comment

The manual always uses the format with multiple dependencies. This only
add an example where is a single dependency to show that this format is
applicable regardless of the number of dependencies.

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Acked-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>