[perl #77682] PATCH: perlunicode.pod fix description of user casing

Thanks, applied as 68585b5ebe5d00d93dc3859b2f1c41cd2646f997 (after a
minor change to make the "for serious hackers only" not consistent with
the other similar notes in the same file).

• [perl #77682] PATCH: perlunicode.pod fix description of user casing by Florian Ragwitz via RT