readme example for Tiered Sharing looks buggy

[simbo1905]

The example code on the readme declares admin twice and doesn't declare 'users`.

    final Map<Integer, byte[]> admins = adminScheme.split(secret);

    final Map<Integer, Map<Integer, byte[]>> admins =
        users.entrySet()
            .stream()
            .collect(Collectors.toMap(Map.Entry::getKey, e -> userScheme.split(e.getValue())));

then we see users used but not declared.

    System.out.printf("%d = %s\n", 1, Arrays.toString(users.get(3).get(1)));

I have sent a PR to fix.