Doc patch for perlsyn, clarification in given/when

Doc patch for perlsyn, clarification in given/when

I had about an hour of über confusion regarding smart matching in a
when, and when I finally clocked on to what the POD was telling me I
thought clarification would be in order. Many agreed :)

The chief change I would make is to use the word 'operands' instead of
'arguments' when referring to the ... and ..., ... && ... etc
sections; this was the major cause of my confusion. Second
clarification is that 'the test' in question is whether to use smart
matching, not the result of using smart matching!

Patch follows; please go ahead and amend as required :)