[Perl/perl5] 047a0e: Add difference between <=> and cmp example

[積丹尼 Dan Jacobson via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 047a0ea72f583771e88b81f628b4e3468b794b37
      
https://github.com/Perl/perl5/commit/047a0ea72f583771e88b81f628b4e3468b794b37
  Author: 積丹尼 Dan Jacobson <jida...@jidanni.org>
  Date:   2021-05-31 (Mon, 31 May 2021)

  Changed paths:
    M pod/perlop.pod

  Log Message:
  -----------
  Add difference between <=> and cmp example

For https://github.com/Perl/perl5/issues/18742