Please add a section on relational database indices and that we recommend to create them manually

[asishallab]

When searching the current online documentation for index I do not get a result and database indices.

It should be made clear that Zendro cannot create indices on foreign key columns out of the box. And that it is highly recommended to create a migration to create these indices.

Please provide an example.

Also check, whether the code-generator warns about indices not being created for foreign keys out of box