Change the wording on self-referential structures

It's fine, you can use them.

Closes #1125

Author: coke

doc/Language/containers.pod6

@@ -273,18 +273,20 @@ Methods generally don't care whether their invocant is in a scalar, so
 
 maps over a list of three elements, not of one.
 
-=head1 Self Reference
+=head1 Self-Referential Data
 
-Complex containers, like Array or Hash and relatives, can contain a reference
-to itself, forming recursive data structures. Please note that very few builtin
-functions and methods will detect infinite loops. It is the responsibility of the
-user to L<handle|/type/Promise#method_in> timeouts.
+Containers types, including C<Array> and C<Hash>, allow you to create
+self-referential structures.
 
     my @a;
     @a[0] = @a;
     put @a.perl;
     # OUTPUT: «((my @Array_75093712) = [@Array_75093712,])␤»
 
+Perl 6 does not prevent you from creating and using self-referential
+data; You may end up in a loop trying to dump the data; as a
+last resort, you can use Promises to L<handle|/type/Promise#method_in> timeouts.
+
 =head1 Type Constraints
 
 Any container can have a type constraint in the form of