[S32/IO] change say to use .gist instead of .Str

Author: felher

S32-setting-library/IO.pod

@@ -450,8 +450,9 @@ the empty list at runtime.)
 
 =item multi say (*@LIST --> Bool)
 
-This is identical to print() except that it auto-appends the C<output-line-separator> after
-the final argument.
+This is identical to print() except that it stringifies its arguments by calling
+C<.gist> on them and auto-appends the C<output-line-separator> after the final
+argument.
 
     Was:    print "Hello, world!\n";
     Now:    say   "Hello, world!";