Change the root directory D8 [docroot > web]
Drupal itself doesn't care about its folder name (at least, not that I've found).  CiviCRM cares, and so does Composer.


When you rename your folder, find the installer-paths section in composer.json (in the webroot) and change docroot to web there.  
You'll also need to change all instances of docroot in civicrm.settings.php.
Rebuild your Drupal cache and flush Civi caches as well.  
If you have absolute paths (that is, not using tokens like [cms.root]) in Civi's Administer » System Settings » Directories or Administer » System Settings » Resource URLs menus, change those too. 
Of course, don't forget to change your web server configuration :)