Update README.md

kyu_4/human_readable_duration_format/README.md

@@ -27,4 +27,6 @@ Different components have different unit of times. So there is not repeated unit
 
 A component will not appear at all if its value happens to be zero. Hence, 1 minute and 0 seconds is not valid, but it should be just `1 minute`.
 
-A unit of time must be used "as much as possible". It means that the function should not return 61 seconds, but `1 minute and 1 second` instead. Formally, the duration specified by of a component must not be greater than any valid more significant unit of time.
+A unit of time must be used "as much as possible". It means that the function should not return 61 seconds, but `1 minute and 1 second` instead. Formally, the duration specified by of a component must not be greater than any valid more significant unit of time.
+
+[Source](https://www.codewars.com/kata/52742f58faf5485cae000b9a/train/python)