update VAT importer

doc/uncloud-manual-2020-08-01.org

@@ -60,6 +60,22 @@ python manage.py migrate
     python manage.py bootstrap-user --username nicocustomer
     #+END_SRC
 
+** Initialise the database
+   While it is not strictly required to add default values to the
+   database, it might significantly reduce the starting time with
+   uncloud.
+
+   To add the default database values run:
+
+   #+BEGIN_SRC shell
+   # Add local objects
+   python manage.py db-add-defaults
+
+   # Import VAT rates
+   python manage.py import-vat-rates
+
+   #+END_SRC
+
 * Testing / CLI Access
   Access via the commandline (CLI) can be done using curl or
   httpie. In our examples we will use httpie.