API page: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Render%21...
Enter a descriptive title (above) relating to class Table, then describe the problem you have found:
First, the documentation is missing a lot of details. Table seems to support #footer and #caption, which are not listed.
Second, the table rows are not being added to the #rows element. I don't think the table in the example would actually render correctly.