Change unified diff command

[rpep]

Puzzled over this one for a while when following the current instructions (not being familiar with using diff and patch).

If a patch requires removal of a file, removing the file + running 'diff -ru' is not sufficient - you need to also add the N flag to get it to treat the removed file as empty which makes it be removed when patch is called.

[ocaisa]

@rpep Your PR targets main rather than develop, can you please switch the target branch (main is protected so I can't merge this)

[rpep]

Apologies, done!