add perl6books.com to faq

Author: stmuk

doc/Language/faq.pod6

@@ -91,6 +91,8 @@ the L<Resources page|https://perl6.org/resources/>.
 You can also consult this
 L<great cheatsheet|http://htmlpreview.github.io/?https://github.com/perl6/mu/blob/master/docs/Perl6/Cheatsheet/cheatsheet.html>.
 
+L<perl6book.com|https://perl6book.com/> contains a list of dead tree books.
+
 Be mindful of publication dates when reading third-party articles. Anything
 published before December, 2015 likely describes pre-release version of Perl 6.