Correct equivalent for split without a pattern (#3988)

* Correct equivalent for split without a pattern

In Perl, split without a pattern is different from split "" — telling users of the former to switch to the latter changes from splitting by words to splitting by characters.

* Update 5to6-perlfunc.pod6

* Update 5to6-perlfunc.pod6

doc/Language/5to6-perlfunc.pod6

@@ -1935,8 +1935,10 @@ also now works as a method: C<"a;b;c".split(';')>
 
 =item split
 
-The zero argument version must now be called with an explicit empty string, as
-described above.
+C<split> now requires a pattern. For the equivalent of Perl's behaviour
+of splitting on whitespace when no pattern is specified, use
+L<words|/routine/words> (or use C<split> with C</\s+/> as the pattern
+and C<:skip-empty> as a named argument).
 
 X<| sprintf - perlfunc>
 =head2 sprintf