Document final steps of "Write the image" procedure in "The OS on icub-head - Installation from pre-built image"

[traversaro]

In the 'Write the image" section in https://icub-tech-iit.github.io/documentation/icub_operating_systems/icubos/installation-from-image/#write-the-image, a few steps are missing that could confused not experience users of clonezilla (like me : ) ).

Personally, I was stopped at the last documented step, i.e. :

select the correct drive and partition for the USB drive (as in step 8) (usually partition is n.1)

I arrived at this form:

As the selected directory was the correct one, I simply pressed Enter, but this resulted in the error "The directory you choose is a Clonezilla dir"

If I typed enter again, I would be brought back to the original form, in a sort of endless loop. The way of exiting for this loop is not to press enter (that will automatically select the "Browse" option in the form), but you need to use the arrow keys to reach the "Done" option and select that one.

After that, you will see many forms, but selecting the default one is ok, except for the "select mode" one:

In Select Mode, the default option is savedisk, but the correct option to select in this case is restoredisk, that needs to be selected with arrow keys. After selecting that, continuing with the default options for the rest of the forms is fine.

[traversaro]

fyi @davidelasagna