improve the migration docs by putting in the password directly

Signed-off-by: szaimen <szaimen@e.mail.de>

migration.md

@@ -42,7 +42,7 @@ The procedure for migrating the files and the database works like this:
         ```
     1. Run the following command to start the conversion:
         ```
-        occ db:convert-type --all-apps pgsql "$PG_USER" 127.0.0.1 "$PG_DATABASE"
+        occ db:convert-type --all-apps --password "$PGDB_PASS" pgsql "$PG_USER" 127.0.0.1 "$PG_DATABASE"
         ```
         **Please note:** You might need to change the ip-address `127.0.0.1` based on your exact installation.<br>
         Further information on the conversion is additionally available here: https://docs.nextcloud.com/server/stable/admin_manual/configuration_database/db_conversion.html#converting-database-type