I am trying to install Bootstrap theme in Drupal 8, but am not able to install it. This was trail to start with drupal 8 themeing. Any help on this welcomed,

I get error message

"The bootstrap theme was not found.
Your version of Drupal is no longer supported. Upgrading is strongly recommended! See the available updates page for more information and to install your missing updates."

I did updates but still same issue.