docs: Update readme

README.md

@@ -7,10 +7,7 @@ You first need to manually use the normal seafile docker image to generate the m
 config files, the superuser, and migrate the databases.
 
 If you additionally wish to use PostgreSQL, you’ll also need to run
-`python manage.py createsuperuser` and `python manage.py syncdb` to migrate that database.
-
-Use `/haiwen/seafile-server-latest/seahub/setenv.sh` to load the environment variables
-needed by `manage.py`
+`python3 manage.py createsuperuser`.
 
 Then you can run this image, and mount the configuration files.