Doc: update end user workflow sections

Try to make it clearer what "adding components"
means and that the Qt 5 installer is used as an
example implementation in these sections.

Update Qt 5 installer screenshots.

Change-Id: I43f104b3a827b4e69313e01405bb088c52c46817
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>