[DOCS] Document that parseUUID consumes its input range

[jpf91]

fixes https://d.puremagic.com/issues/show_bug.cgi?id=12148

(Although right now I'm not sure if this behavior is useful as parseUUID processes the complete input, unlike the normal parse functions.)

[monarchdodra]

How about making that a documented unittest? Also, (arguably), I'd prefer s/its input range/its argument/, and s/This parser/Like most parsers/

If you disagree, or don't feel like doing it, do tell me, so I can merge regardless.

[jpf91]

I adjusted the comment. I'd like to keep the example code after the comment and not in the examples section as it's meant as a clarification of the comment. That's why I didn't use documented unit tests.