Adds POD6 to README.

Closes #907 when accepted (along with the rest of the commits).

README.md

@@ -29,7 +29,8 @@ you wish to run the library. You can also run `script/bootstrap` to fetch them a
 * [.asciidoc, .adoc, .asc](http://asciidoc.org/) -- `gem install asciidoctor` (http://asciidoctor.org)
 * [.pod](http://search.cpan.org/dist/perl/pod/perlpod.pod) -- `Pod::Simple::XHTML`
   comes with Perl >= 5.10. Lower versions should install Pod::Simple from CPAN.
-
+* [.pod6](https://docs.perl6.org/language/pod) -- No additional
+  dependency. 
 
 Installation
 -----------