Provide response for naked fhir request

Currently https://fhir.qa2.aws.openconceptlab.org/ returns a 404, though https://fhir.qa2.aws.openconceptlab.org/fhir/ returns a JSON response informing the client that this is the "base" of the FHIR service. Let's decide what the response to https://fhir.qa2.aws.openconceptlab.org/ should be and implement.