Specify the range for integrators progress

EdgeAndPropertyHierarchy/progress/progress.json

 {
-  "description": "The progress an Item made. The number could be a (rounded) percentage or a count of a (potentially unknown) total.",
+  "description": "The progress an Item made. Encoded as a float number from 0.0 to 1.0.",
   "type": "float"
-}
\ No newline at end of file
+}