Improve Docker documentation

See https://github.com/nijel/weblate-docker/issues/1

[CI skip]
Signed-off-by: Michal Čihař <michal@cihar.com>

docs/admin/install.rst

@@ -807,17 +807,23 @@ Example for Mac OS, similar on Windows, Linux, ...
 
     docker-compose build
 
-6. Create Weblate database:
+6. Start Weblate containers:
 
 .. code-block:: sh
 
-    docker-compose run migrate
+    docker-compose up
 
-7. Start weblate containers:
+7. Create Weblate database:
 
 .. code-block:: sh
 
-    docker-compose up
+    docker-compose run weblate-web migrate
+
+8. Create admin user:
+
+.. code-block:: sh
+
+    docker-compose run weblate-web createadmin
 
 Enjoy your Weblate deployment, it's accessible on port 8000.