/**
  * Add a new user to a project.
  *
  * @param string $email An email address.
  * @param string $role  One of User::ROLE_ADMIN or User::ROLE_VIEWER.
  *
  * @return ProjectUser
  */
 public function addUser($email, $role)
 {
     $body = ['email' => $email, 'role' => $role];
     return ProjectUser::create($body, $this->getLink('access'), $this->client);
 }