add to description of OS state (#19764)

Author: tfitzmac

specification/compute/resource-manager/Microsoft.Compute/stable/2022-03-01/ComputeRP/image.json

@@ -404,7 +404,7 @@
         },
         "osState": {
           "type": "string",
-          "description": "The OS State.",
+          "description": "The OS State. For managed images, use Generalized.",
           "enum": [
             "Generalized",
             "Specialized"