code: func (s *UsersService) GetByID(ctx context.Context, id int64) (*User, *Response, error) {
  	u := fmt.Sprintf("user/%d", id)
  	req, err := s.client.NewRequest("GET", u, nil)
  	if err != nil {
  		return nil, nil, err
  	}
  
  	user := new(User)
  	resp, err := s.client.Do(ctx, req, user)
  	if err != nil {
  		return nil, resp, err
  	}
  
  	return user, resp, nil
  }
docs: // GetByID fetches a user.
  //
  // Note: GetByID uses the undocumented GitHub API endpoint /user/:id.