code: func (s *RepositoriesService) EnablePages(ctx context.Context, owner, repo string) (*Pages, *Response, error) {
  	u := fmt.Sprintf("repos/%v/%v/pages", owner, repo)
  	req, err := s.client.NewRequest("POST", u, nil)
  	if err != nil {
  		return nil, nil, err
  	}
  
  	// TODO: remove custom Accept header when this API fully launches.
  	acceptHeaders := []string{mediaTypeEnablePagesAPIPreview, mediaTypePagesPreview}
  	req.Header.Set("Accept", strings.Join(acceptHeaders, ", "))
  
  	enable := new(Pages)
  	resp, err := s.client.Do(ctx, req, enable)
  	if err != nil {
  		return nil, resp, err
  	}
  
  	return enable, resp, nil
  }
docs: // EnablePages enables GitHub Pages for the named repo.
  //
  // GitHub API docs: https://developer.github.com/v3/repos/pages/#enable-a-pages-site