clarify shortcut key names

[practik]

@ysard, thank you for fixing these bugs so quickly!

I just took a quick look at the commit that fixed #20 and #21, and I have two more suggestions:

Instead of maj+tab, maybe ⇧+tab would be better for users who don't speak French.

You might also want to change suppr– I noticed that @scheinercc was confused by this in #11 (he wrote: "There is no super key"). Unfortunately I don't know of any symbol for this one, but since the rest of the preferences are in English, you could change it to delete or just del.

[ysard]

Sorry I missed the problem with the delete key on MacOS, this should be solved with 87fb633.