Update to dd-api-spec.yaml regarding UMLS api key.

dd-api-spec.yaml

@@ -1,7 +1,7 @@
 openapi: 3.0.3
 info:
   title: Data Distillery API
-  description: The Data Distillery API provides REST endpoints that return results from queries against an instance of [Data Distillery](https://github.com/TaylorResearchLab/CFDE_DataDistillery), which is a deployment of the [Unified Biomedical Knowledge Graph (UBKG)](https://ubkg.docs.xconsortia.org/). To prevent exceeding service timeouts or payload limits, some endpoints are throttled in both execution time and in the size of its response payload--e.g., to a maximum execution time of 15 seconds and a maximum payload of 9 MB. The Data Distillery API requires an API Key.
+  description: The Data Distillery API provides REST endpoints that return results from queries against an instance of [Data Distillery](https://github.com/TaylorResearchLab/CFDE_DataDistillery), which is a deployment of the [Unified Biomedical Knowledge Graph (UBKG)](https://ubkg.docs.xconsortia.org/). To prevent exceeding service timeouts or payload limits, some endpoints are throttled in both execution time and in the size of its response payload--e.g., to a maximum execution time of 15 seconds and a maximum payload of 9 MB. NOTE - The API requires an Authorization key in the request header in format "UMLS-Key[space][apikey]", where apikey is the API key for a UMLS licensee acount.
   version: "2.0"
   contact:
     name: GitHub repository