docs(readme): add ACL management feature documentation}
- Document ACL user list view with status, current user indicator, and rules summary - Document create, edit, and delete user management via dialog with chip-based rule editing - Document chip inputs for commands, key patterns, and pub/sub channels - Document deny highlighting for commands starting with `-` prefix - Document default user warning alert for risk of locking out connections - Document save confirmation dialog for ACL changes - Note consistent implementation across Angular, React, and Vue GUIs