Buf.reallocate example improved.

Show that the buffer can be enlarged.

Author: fluca1978

doc/Type/Buf.pod6

@@ -71,6 +71,10 @@ returns the altered C<Buf>.
     $b.reallocate(5);
     say $b.perl;  # OUTPUT: «Buf.new(0,1,2,3,4)␤»
 
+    $b = Buf.new( 1..3 );
+    $b.reallocate( 10 );
+    $b.perl.say; # OUTPUT: «Buf.new(1,2,3,0,0,0,0,0,0,0)␤»
+
 =head2 method push
 
     method push( $elems )