I'm using this guide.
At this point
$ docker run --rm -v drupal-sites:/temporary/sites drupal cp -aRT \
/var/www/html/sites /temporary/sites
$ docker run --name some-drupal --link some-postgres:postgres -d \
-v drupal-modules:/var/www/html/modules \
-v drupal-profiles:/var/www/html/profiles \
-v drupal-sites:/var/www/html/sites \
-v drupal-themes:/var/www/html/themes \
drupal
I'm not sure how drupal-sites volume is used. In the first instruction i understood that: we copy /var/www/html/sites in /temporary/sites dir, after that we map /temporary/sites in the drupal-site volume. After running we delete the container.
In the second instruction We remap the drupal-sites volume to /var/www/html/sites.
What are we doing with drupal-site volume and with /temporary/sites?