Add Raku One-Liners book (#3440)

free-programming-books.md

@@ -2000,6 +2000,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Perl 6 at a Glance](https://perl6.online/perl6-at-a-glance/) - Andrew Shitov (HTML) (PDF)
 * [Perl 6 Introduction](http://perl6intro.com)
 * [Perl 6 Programming](https://en.wikibooks.org/wiki/Perl_6_Programming) - Wikibooks
+* [Raku One-Liners](https://deeptext.media/raku-oneliners) - Andrew Shitov (PDF)
 * [Think Perl 6](http://greenteapress.com/thinkperl6/thinkperl6.pdf) - Laurent Rosenfeld, with Allen B. Downey (PDF)
 * [Using Perl 6](https://github.com/perl6/book/) (:construction: *project is dead*)