Roles only require a single directory (e.g. `tasks`), don't require meta dir

From a reader's email:

> I found an error or confusing part that needs clarification on p132 (Role scaffolding):
>
> "There are only two directories required to make a working Ansible role:"
>
> ```
> role_name/
> meta/
> tasks/
> ```
>
> However, the documentation seems to say otherwise (https://docs.ansible.com/ansible/latest/user_guide/playbooks_reuse_roles.html#role-directory-structure):
>
> "Roles must include at least one of these directories, however it is perfectly fine to exclude any which are not being used."
>
> So you can indeed have a role with only a tasks folder and the meta folder can be left out.
>
> Sincerely
> Daniel S

True! I'll have to fix up the book's statement.

Start with the role scaffolding section on page 132 and compare its quoted directory example with the Ansible role-directory documentation linked in the issue. Update the book's statement so it accurately describes the minimum required structure, then check that the surrounding explanation remains consistent.

Written by the indexing model from the issue text.