README.md in trackler-2.2.1.75

- old
+ new

@@ -1,13 +1,28 @@
 # Sum Of Multiples
 
-Given a number, find the sum of all the multiples of particular numbers up to
+Given a number, find the sum of all the unique multiples of particular numbers up to
 but not including that number.
 
-If we list all the natural numbers up to but not including 20 that are
-multiples of either 3 or 5, we get 3, 5, 6 and 9, 10, 12, 15, and 18.
+If we list all the natural numbers below 20 that are multiples of 3 or 5,
+we get 3, 5, 6, 9, 10, 12, 15, and 18.
 
 The sum of these multiples is 78.
+
+## Exception messages
+
+Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to
+indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not
+every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include
+a message.
+
+To raise a message with an exception, just write it as an argument to the exception type. For example, instead of
+`raise Exception`, you shold write:
+
+```python
+raise Exception("Meaningful message indicating the source of the error")
+```
+
 
 ## Submitting Exercises
 
 Note that, when trying to submit an exercise, make sure the solution is in the `exercism/python/<exerciseName>` directory.
 