Make it clear what Any.hash does.

See issue #1731.
As of source code in moar-2017.12.

Author: fluca1978

doc/Type/Any.pod6

@@ -375,9 +375,20 @@ Coerce the invocant to L<Hash>.
 
 Defined as:
 
-    method hash(--> Hash:D) is nodal
+    proto method hash(|) is nodal
+    multi method hash(Any:U: --> Hash:D)
+    multi method hash(Any:D: --> Hash:D)
 
-Coerce the invocant to L<Hash>.
+Creates a new L<Hash|/type/Hash>, empty in the case the invocant is
+undefined, or coerces the invocant to an C<Hash> in the case it is
+defined.
+
+=begin code
+my $d; # $d is Any
+say $d.hash; # OUTPUT: {}
+$d.append: 'a', 'b';
+say $d.hash; # OUTPUT: {a => b}
+=end code
 
 =head2 method Slip