Install composer dependencies with ddev composer install and commit composer.lock and generated files in the web folder. If Drupal adds additional database credentials in settings.php, these should not be committed and can be discarded.
Install javascript dependencies with npm install and commit the package-lock.json file.
Install Drupal with ddev drush site-install / ddev drush si and export the default configuration with ddev drush config-export / ddev drush cex.
Log in to CircleCI with your Github credentials, select "wunderio" and enable your project.
Watch your project build, the CircleCI output has a link to your deployed environment.