Clarifies example

Thanks to @raiph in
https://stackoverflow.com/a/54635282/891440. This (hopefully) closes #2620

doc/Type/Mu.pod6

@@ -252,9 +252,10 @@ and then manipulate the clone as needed, before returning it.
 
 =begin code
 class Bar {
+    has $.quux;
     has @.foo = <a b>;
     has %.bar = <a b c d>;
-    method clone { nextwith :foo(@!foo.clone) :bar(%!bar.clone) }
+    method clone { nextwith :foo(@!foo.clone), :bar(%!bar.clone), |%_  }
 }
 
 my $o1 = Bar.new;
@@ -264,10 +265,15 @@ with my $o2 = $o1.clone {
 }
 
 # Hash and Array attribute modifications in clone do not affect original:
-say $o1; # OUTPUT: «Bar.new(foo => ["a", "b"], bar => {:a("b"), :c("d")})␤»
-say $o2; # OUTPUT: «Bar.new(foo => ["Z", "Y"], bar => {:X("W"), :Z("Y")})␤»
+say $o1;
+# OUTPUT: «Bar.new(quux => 42, foo => ["a", "b"], bar => {:a("b"), :c("d")})␤»
+say $o2;
+# OUTPUT: «Bar.new(quux => 42, foo => ["Z", "Y"], bar => {:X("W"), :Z("Y")})␤»
 =end code
 
+The C<|%_> is needed to slurp the rest of the attributes that would have been
+copied via shallow copy.
+
 =head2 method new
 
     multi method new(*%attrinit)