Document on data structures is completed.

I would be happy as a clam if this closed an issue, but it only means
a feeble tick in the humongous #114. However, closer to the end, with
just a couple of pages to go...

doc/Language/structures.pod6

@@ -414,7 +414,8 @@ my @lines = $fh.lines;
 close $fh;
 say @lines[0]; # no problem!
 
-Also good:
+We can also use any function whose side effect is reification, like C<.elems>
+mentioned above:
 
 =for code
 my $fh = "/tmp/bar".IO.open;