[Perl/perl5] 95ba35: Document SvSHARED_SHASH

[Karl Williamson via perl5-changes]

  Branch: refs/heads/smoke-me/khw-pr_api6
  Home:   https://github.com/Perl/perl5
  Commit: 95ba35042bbef6d70cb00f2c0f2acc8e81d04af2
      
https://github.com/Perl/perl5/commit/95ba35042bbef6d70cb00f2c0f2acc8e81d04af2
  Author: Karl Williamson <k...@cpan.org>
  Date:   2020-11-22 (Sun, 22 Nov 2020)

  Changed paths:
    M sv.h

  Log Message:
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  Document SvSHARED_SHASH