Update query params for GET /files endpoint (#719)

Update query params for GET /files endpoint (#719)

Author: RyanDotsikas

xero_files.yaml

@@ -49,7 +49,16 @@ paths:
             - Name
             - Size
             - CreatedDateUTC
-            example: "CreatedDateUTC DESC"
+            example: "CreatedDateUTC"
+        - in: query
+          name: direction
+          description: sort direction
+          schema:
+            type: string
+            enum: 
+            - ASC
+            - DESC
+            example: "ASC"
       responses:
         '200':
           description: search results matching criteria