amplify the substr-rw examples

Author: tbrowder

doc/Type/Str.pod6

@@ -903,14 +903,21 @@ one does this:
 
     my $string = "abc";
     $string.substr-rw(1, 1) = "z";
-    $string.say;                    # OUTPUT: «azc␤»
+    $string.say;                         # OUTPUT: «azc␤»
+    
+Note that new characters can be inserted as well:
 
-C<substr-rw> also has a function form, so the above example can also be
+    $string.substr-rw(2, 0) = "-Zorro-"; # insert new characters BEFORE the character at index 2
+    $string.say;                         # OUTPUT: «az-Zorro-c␤»
+
+C<substr-rw> also has a function form, so the above examples can also be
 written like so:
 
     my $string = "abc";
     substr-rw($string, 1, 1) = "z";
-    $string.say;                    # OUTPUT: «azc␤»
+    $string.say;                          # OUTPUT: «azc␤»
+    substr-rw($string, 2, 0) = "-Zorro-";
+    $string.say;                          # OUTPUT: «az-Zorro-c␤»
 
 It is also possible to alias the writable reference returned by C<substr-rw>
 for repeated operations: