Clarify documentation on how to Select (and delete) multiple files

[aloboa]

I have tried dude as suggested in https://github.com/qarmin/czkawka/issues/1265

Thanks.

It is hard to see how to delete the listed files (or some of them).

Besides the video, a simple Help text would be much appreciated, as well as a direct link to the video from the Help tab

[PJDude]

dude allows to delete (or process another way) duplicate files. Just follow General usage and use needed actions in context menus. Non-duplicate files are shown and not processed.