re-order Docker section

post-debootstrap-installer.sh

@@ -64,6 +64,13 @@ echo 'nameserver 1.1.1.1
 nameserver 8.8.8.8' > /etc/resolv.conf
 
 
+### Docker
+# has to be executed before the users section,
+# because otherwise the docker group doesn't exist
+
+apt-get -y install docker-ce
+
+
 ### users
 
 apt-get -y install sudo
@@ -82,11 +89,6 @@ for key in /hardware-setup/authorized_keys/*; do
 done
 
 
-### Docker
-
-apt-get -y install docker-ce
-
-
 ### administration tools
 
 apt-get -y install \