Documentation on the Terminology Services should document MimeTypeTerminologyService

[ewoutkramer]

Is your feature request related to a problem? Please describe.
We have created a new MimeTypeTerminologyService that you can use (in combination with a MultiTerminologyService) to validate bcp-13. However, our documentation at https://docs.fire.ly/projects/Firely-NET-SDK/validation/terminology-service.html# does not talk about it.

Describe the solution you'd like
We should mention the MimeTypeTerminologyService and have an example, combining it with another common ITerminologyService.