Add missing information about accessing DB

[tvedeane]

This PR tries to solve issues discussed briefly here: https://forum.exercism.org/t/adds-database-class-to-objectrelationalmapping-cs/16314

[github-actions]

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[ErikSchierboom]

I appreciate that this is confusing. The proper fix is to move the Database class out of the tests file (https://github.com/exercism/csharp/blob/main/exercises/concept/object-relational-mapping/ObjectRelationalMappingTests.cs#L83) and into it's own, separate file. It then needs to be added to the files.editor key in the .meta/config.json file (https://github.com/exercism/csharp/blob/main/exercises/concept/object-relational-mapping/.meta/config.json).

[tvedeane]

Thanks for explaining @ErikSchierboom . I followed your suggestions, but I wasn't sure about the details. So this should be definitely properly reviewed (and ideally tested).

[ErikSchierboom]

Thanks