Adds example for destructuring hashes in pointy loops

Closes #1466

Author: JJ

doc/Type/Signature.pod6

@@ -714,6 +714,14 @@ While the destructuring of a hash is its pairs:
         $x andthen $y andthen $z andthen True
     }
 
+Pointy loops can also destructure hashes, allowing assignment to variables:
+
+    my %hhgttu = (:40life, :41universe, :42everything);
+    for %hhgttu -> (:$key, :$value) {
+      say "$key → $value";
+    }
+    # OUTPUT: «universe → 41␤life → 40␤everything → 42␤»
+
 In general, an object is destructured based on its attributes. A common idiom
 is to unpack a L<C<Pair>>'s key and value in a for loop: