add example of an interpolating heredoc

Author: tbrowder

doc/Language/quoting.pod6

@@ -340,6 +340,23 @@ some multi line
 
 Heredocs include the newline from before the terminator.
 
+To allow interpolation of variable use the C<qq> form, but you will then have to escape some meta characters such as
+C<{}$"'> and others.  For example:
+
+  my $f = 'db.7.3.8';
+  my $s = qq:to/END/;
+  option \{
+      file \"$f\";
+  \};
+  END
+  say $s;
+
+would produce:
+
+  option {
+      file "db.7.3.8";
+  };
+
 =head1 Regexes
 
 For information about quoting as applied in regexes see the L<regular