Document Any.pairs a little more.

Documentation comes from the source of Any shipped with
Rakudo version 2017.11 built on MoarVM version 2017.11

See issue #1731

Author: fluca1978

doc/Type/Any.pod6

@@ -709,11 +709,19 @@ TODO
 
 Defined As:
 
-    method pairs(--> List)
+    multi method pairs(Any:U:)
+    multi method pairs(Any:D:)
 
-Returns an empty List.
+Returns an empty L<List> if the invocant is undefined, otherwise
+converts the invocant to a L<List> via the C<list> method
+and calls L<List.pairs> on it:
 
     say Any.pairs; # OUTPUT: «()␤»
+    my $a;
+    $a.pairs;      # OUTPUT: «()»
+    $a = Any.new;
+    $a.pairs;      # OUTPUT: «(0 => Any.new)»
+
 
 =head2 method antipairs